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straight 6 engine swap... 23" to 25"


Guest pyrodork

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Guest pyrodork

i have a 37 plymouth with a bad engine. i thought about repairing/rebuilding, but 1) i've never done that before and 2) money, tools, money... money.

anyway, i found a rebuilt desoto engine for a price i'm willing to pay. the only thing is, my current engine is 23" long (likely the 201... but i'm not exactly sure... long story), and the desoto engine is 25" long (236.6?). i currently have no extra clearance for a longer engine.

i have heard a trick about reversing the radiator housing to provide the extra room needed, but just by visualizing it, i can't see how that would do anything. does someone have the experience of doing this; maybe even a website tutorial with pictures? or am i just out of luck until i find a 23" block?

thanks!

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Check out this website P15-D24 Homepage , others have done this very swap, with some modifications it can be done.

Interestingly, in Canada, all Mopars cars and trucks had 25 inch flathead 6s, they did not market or make the 23.5 inch 201,218 or 230s, they had 218,228,237,251,265, all with a 25 inch block.

You will have to move your front motor mounts forward, and somehow move the rad ahead, or eliminate the fan, and go with an electric pusher fan, which you can buy in the 6 volt type if you need.

The 251 will give your Plymouth some extra boost, having probably an extra 30-40 HP, that you will notice.....

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Guest pyrodork

joe, you are a bit far from me, but i'll keep that in mind.

fred, i've been searching that website for hours. all i see is reference that people have done it and that a "quick search" should pull up any info needed. i haven't found a thing relating to the 23 to 25 swap. having to do that stupid "captcha" every time i want to do a search is giving me a headache.

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joe, you are a bit far from me, but i'll keep that in mind.

fred, i've been searching that website for hours. all i see is reference that people have done it and that a "quick search" should pull up any info needed. i haven't found a thing relating to the 23 to 25 swap. having to do that stupid "captcha" every time i want to do a search is giving me a headache.

Contact Don Coatney, on P15-D24 he has done this very swap, He can give you some info with substance on this topic...........Fred

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That swap is apparently much easier on vehicles that were sold in both the US and Canada after Canadian engine production started. However for a 1930s Plymouth I think there would have to be major changes made to the car to fit a 2" longer engine under the hood. For one thing, pre-1939 or so, you can't just flip the radiator mount around and the front frame cross member would probably also need major surgery.

You can bolt any 1933-59 US built Plymouth or Dodge 6 cylinder passenger car engine into your car without modifications and there should be plenty of those still available. I'd pass on trying to put that DeSoto engine into your car...

If you care about judging, the Plymouth Owners Club will check the engineering code on the engine, so you'd want an engine with a number starting with P4. Not sure about AACA as the judges there might not know what to look for.

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If it were a Canadian 37 Plym or Dodge, which shared the same body, in Canada, it would have come witha 25 inch engine.

So yours beinga ply, this could be doable, exactly whats needed, will be your research to find out.

The idea of going toa say late 50s, 230 23.5 inch engine could be great, as those came with cloes toa 130 hp stock, witha higher compression ratio to boot. You would notice some more pep with that.....

PS go non P15-D24, and post some questions, lots of traffic on there, with a lot of knowledgable Guys...

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  • 2 weeks later...
Guest pyrodork

just out of curiosity, if i'm going to change the engine out, how hard would it be to change to a 318, 340, 360 instead? motor mounts are obvious, but i'm more worried about electrical, gauges, pedals... overall functioning. i often find these with small block 340/360 mopar engines in them, but not up close so i can examine.

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Steering box is usually in the way. The smalll block A' body used an exhaust manifold that rises up to clear the OEM power steering on the driver side that might help. I think you will still need to offset the engine a bit.

It is no big deal to offset the engine as long as the centerlines of the crankshaft and the pinion shaft are parallel. (both up and down and side to side). If you try to aim the engine at the rear end you will get a vibration.

If you are going in that deep why not look into a Mustang II or a Fatman IFS kit.

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Guest pyrodork

eventually, but one thing at a time. the guy i bought the car from had a 340 or 360 with j heads he was going to put in it. plus 2 4-speed trannies and a rear end from a 73 challenger for $600. not sure if he still has them, but if i'm going to spend the money, why don't i spend it on something bigger?

alternate plans are to either get that desoto engine or resleeve the cylinders in the one i've got and put in new rods and pistons. i started thinking about the bigger engine because if i get the bigger desoto (ideally because of slightly more hp), i'll have to modify things anyway. might as well get an engine that will give me a lot more hp, right? it makes sense to me.

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One thing at a time may work for you, but remember that one thing leads to another.

There would be an order to things, no sence in building your motor mounts if you are going too change suspension later.

If you are going to race the thing then by all means get the highest HP that you can. I have built several of these things and I like four speeds. The problem with a built engine and a manual tranny is the drivability. Cammed up motors with manual trannys dont go slow very well. So if you are doing parades or drive thru car shows they are a *****.

The Hemi in my 28 Dodge wont travel at idle as the cam gets to violent on the running gear so clutch in, clutch out constantly. I have a couple of cars that do this and I make my kids drive them.

Here is a picture of three of my cars inside the Oregon State Pen. They do an invitational car show every June. I made the daughters drive...HA-HA.

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If it were a Canadian 37 Plym or Dodge, which shared the same body, in Canada, it would have come witha 25 inch engine.

So yours beinga ply, this could be doable, exactly whats needed, will be your research to find out.

The idea of going toa say late 50s, 230 23.5 inch engine could be great, as those came with cloes toa 130 hp stock, witha higher compression ratio to boot. You would notice some more pep with that.....

PS go non P15-D24, and post some questions, lots of traffic on there, with a lot of knowledgable Guys...

No, Chrysler Canada did not open their engine plant until late 1937. Thus 1938 and up Canadian-built vehicles used the 25" block. 1933 to 1937 Canadian-built Plymouths used American-built 23" block Plymouth engines.

Bill

Toronto, ON

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Guest pyrodork
One thing at a time may work for you, but remember that one thing leads to another.

There would be an order to things, no sence in building your motor mounts if you are going too change suspension later.

If you are going to race the thing then by all means get the highest HP that you can. I have built several of these things and I like four speeds. The problem with a built engine and a manual tranny is the drivability. Cammed up motors with manual trannys dont go slow very well. So if you are doing parades or drive thru car shows they are a *****.

The Hemi in my 28 Dodge wont travel at idle as the cam gets to violent on the running gear so clutch in, clutch out constantly. I have a couple of cars that do this and I make my kids drive them.

Here is a picture of three of my cars inside the Oregon State Pen. They do an invitational car show every June. I made the daughters drive...HA-HA.

wow! let's see that rat! (i'd like to hype up my new 29 {maybe 30?} rusty ford stakebed at a later point in time; as 45mph top speed isn't too thrilling on the highway (actually found a 100hp late 40's ford flathead v8, stuck, for $100 that i'm thinking about), but i'd really just like to get her moving right now. same with the plymouth, for that matter. eventually planning to make a roadster stakebed with a folding top (but $$$$$$$$)!

i do like speed... so maybe upgrading the suspension on the plymouth is ideal? or just throw an engine in there to have fun while budgeting for the big deal? thing is, i have to throw a lot of money down regardless. maybe modify the motor mount now and upgrade the suspension when i can afford it? i don't mind the clutch up-down so much.

question remains, though... would it mostly be upgrading the throttle linkage and electrical to make it work once it's in? i honestly have no idea.

Edited by pyrodork (see edit history)
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If money is an issue think carefully about making any changes. It may look cheaper but it won't be because one thing leads to another.

The cheapest way out would be to rebuild the engine you have or if the rod is sticking through the block, find another Plymouth/Dodge engine. They aren't that rare and a lot of guys are changing them out.

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  • 3 weeks later...
Guest pyrodork

The cheapest way out would be to rebuild the engine you have or if the rod is sticking through the block, find another Plymouth/Dodge engine. They aren't that rare and a lot of guys are changing them out.

i think that's what i'm going to end up doing. the block looks good, but i gotta loosen up the crank to get that bent rod out. i figure that i'll at least get the one cylinder resleeved (or should i do them all at once?), new rods/bearings/pistons/rings/gaskets... then see where i end up.

as a backup, i found someone nearby selling a block, but he hasn't had any bites in a year or two.

i'm kinda stuck on which parts to get, though... since my engine does not appear to be original. that "specify model 219" tag is getting to me, too, since i'm aware of a 218 engine, but not a 219.

can't really work on the ply so much right now. got a model AA ford i'm trying to run (not drive right now... just run!). those tire/tube assemblies get mighty expensive when used isn't really an option! money is still tight... but on the bright side, i should have a college degree in june!

Edited by pyrodork (see edit history)
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i think that's what i'm going to end up doing. the block looks good, but i gotta loosen up the crank to get that bent rod out. i figure that i'll at least get the one cylinder resleeved (or should i do them all at once?), new rods/bearings/pistons/rings/gaskets... then see where i end up.

as a backup, i found someone nearby selling a block, but he hasn't had any bites in a year or two.

i'm kinda stuck on which parts to get, though... since my engine does not appear to be original. that "specify model 219" tag is getting to me, too, since i'm aware of a 218 engine, but not a 219.

can't really work on the ply so much right now. got a model AA ford i'm trying to run (not drive right now... just run!). those tire/tube assemblies get mighty expensive when used isn't really an option! money is still tight... but on the bright side, i should have a college degree in june!

"model 219" refers to a model number given to an engine, less accessories, by the parts department. If, say, 1949 through 1953 Plymouths used the same engine, although the Plymouth model numbers change each year, the engine model number would be the same. "Less accessories" means no manifolds, generator, carburetor, wiring or oil filter.

I have a number of Canadian parts books, but Chryco did not start listing the model numbers until 1951. The lowest model number listed in 1951 is model 222, used on US built P22, P23, D39, D40, SP22 and SP23. Canadian-built versions used model 401 engines. Model 222 is also listed in the 1953-54 parts book for the US-built 1953 and early 1954 Plymouth.

The tag also means the engine was rebuilt, or at least part of it was. Will have to determine what size a model 219 is and that will help determine the con rods, etc. needed. For the pistons, determine the diameter of what you have now. The cylinder bores should be 3.125" or 3.25". Anything slightly larger will tell if the cylinders have been bored, and by how much.

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Guest pyrodork
"model 219" refers to a model number given to an engine, less accessories, by the parts department. If, say, 1949 through 1953 Plymouths used the same engine, although the Plymouth model numbers change each year, the engine model number would be the same. "Less accessories" means no manifolds, generator, carburetor, wiring or oil filter.

I have a number of Canadian parts books, but Chryco did not start listing the model numbers until 1951. The lowest model number listed in 1951 is model 222, used on US built P22, P23, D39, D40, SP22 and SP23. Canadian-built versions used model 401 engines. Model 222 is also listed in the 1953-54 parts book for the US-built 1953 and early 1954 Plymouth.

The tag also means the engine was rebuilt, or at least part of it was. Will have to determine what size a model 219 is and that will help determine the con rods, etc. needed. For the pistons, determine the diameter of what you have now. The cylinder bores should be 3.125" or 3.25". Anything slightly larger will tell if the cylinders have been bored, and by how much.

that's interesting! it's odd, though, from the history of the vehicle i've received. regardless, i gots what i gots.

sounds like my 219 may be late 40's to early 50's. judging from a photo i took a few months ago with a tape measure, the bore size appears to be 3.25". my photo doesn't show the measure going to exactly 3.25, but it's close enough to determine. it shows 3 3/16" but not counting the extra mm's that the tip of the tape gives you.

now to find out exactly what size the 219 is. my carter carb model is D6G1, which did cause a problem when i ordered a rebuild kit for a 37 plymouth. i'm not sure if that gives any kind of hint, but perhaps it was a package deal with the engine and the carb was always with it?

post-74472-143138884871_thumb.jpg

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  • 11 years later...
On 2/24/2012 at 8:36 AM, JACK M said:

I can certianly appreciate that one has to be funded to have fun with these old cars.

You must pay to play !!

Wheather its in parts OR labor OR time. (mostly all three)

Remember me? I’m the guy from Tacoma, Washington who ended up with the 1928-1929-19whatever Fargo Express Panel delivery from Onalaska, Wa.

There is no question regarding whether or not the trucks bones are good enough to rebuild because even the bones are rotten.

But, there are those who take pride in knitting sweaters for the homeless or even inviting them into their home for a meal, a nap and a tour including their jewelry chest and silverware drawer.
I won’t…….but I am as gullible as these poor souls because I feel a need to reclaim the dignity of every old, rejected, neglected, abused and abandoned car or truck I see……and the Fargo meets or exceeds every one of these reclusive reprobates.

A mechanical psychologist, or an even a lowly exhaust system proctologist I am not……but I do peruse the forums related to this stuff, and I seem to always see some of the same names,  namely yours, Fargoguy, 30Dodgepanel and Rusty_OTool showing up on threads as far back (2018) as this one.

And it seems like you folks have done a lot of research on, and show a truly hobbyistic sort of interest in the old Dodge…..or in my case,Fargo, trucks.

I have stripped the Fargo down to the bare frame and am in the process of making the patterns I need to restore the wood and metal parts of the body to a condition identifiable as a truck.

The engine, which I believe to be a Chrysler 75 or 80 series, but can’t be sure because the head gasket was stolen and there are too many 25”, flat head 6 engines used in these  with the top mounted distributor to guess it’s true size or model.

Regardless, the engine is locked up, has been soaking in a ATF/acetone mixture for over a month, and shows no sign of turning free. Besides, the cylinder bores of at least three cylinders seems to be deeply rust pitted, the distributor, water pump, oil pump and carburetor will most probably need replacement, and the head has broken in several places and has been welded back together. All-in-all, I did not think the engine is, dollar and dependability wise, repairable or worth a complete rebuild. And, I have been unable to find a bell housing with throw out and pedals and transmission with driveshaft which will fit the 1928-1929 flathead 6 cylinder engine.

So, I have bought the complete engine, transmission and drive shaft taken from a 1951 Dodge pickup. 
The complete setup cost $300.00 and the gas for a F-250 pickup driven to Oregon to pick up the parts. 
So, here is the deal, and the underlying reason I’m rattling you fellows chain…..

The engine presently in the truck is a 25” flathead 6 cylinder which I want to replace with the 1951 model Dodge pickup engine and transmission, which is a 23” block.

I do realize that I have a four inch difference distance in the width of the (wider) rear engine mounts on the 25” engine, and the (narrower) mounts on the, what I think to be, 218 CI newer engine.

This difference I think I can handle by using two, 2” square pieces of tubular steel to extend the transmission mounts on the engine to the width of the frame mounts in the truck. It seems as though there won’t be a major problem mating the bolt holes in the frame mounts to those threaded into the rear engine mounts on the transmission.

The difference in length of the engines is made a bit more complicated by the additional depth of the bell housing on the old engine, as necessitated by the longer starter bendix, and the beefed up construction of its front motor mounts…….a removable steel plate on the newer engine, and built into the timing gear cover on the old engine.

This will make it necessary to move the front engine mounts rearward, toward the cab, about five inches. Since there is no crossmember on the frame at this location, I am thinking about fabricating a front mount using chain rather than weakening the already badly rusted frame by drilling to bolt on a metal adaptor or welding to fabricate one.

Since the has neither a transmission, it’s related pedals, and no floorboards, I see no real problem in making a set of floor boards built around the location of those on the newer engine, and inclusion of a gas pedal, salvaged from my 1923 Dodge roadster build, as well as the floor mounted plunger on the newer starter,  to compensate for the push button operated starter used on the 1929 engine.

I am having difficulties finding a set of lines used to connect the oil filter canister to the engine block on the 1951 model engine and, I suppose, may have to either fabricate a new set myself or pay someone to do it for me.

The brake master cylinder from the 1929 engine was frozen and completely locked up, but sheer will power, a MAP torch and a large hammer helped it be disassembled and revealed that the old master cylinder body appears to be usable with the 1951 transmission mounts, and, with a good honing of the bore, should work with no modification or adapters needed.

I am still in need of a steering wheel with a keyed, 1”, slightly tapered hole where it fits over the shaft in the steering column.

Golly gee fellows, this sure is a whole lot of letters, words, sentences and paragraphs to include in a single post which is made for the sole purpose of saying…….”Any help offered will be greatly appreciated”…..but I take great pride in making use of every pixel, of every letter, my hard working dad had instilled into my numb skull………..😵‍💫.

 

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Edited by Jack Bennett (see edit history)
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I don't think 23" vs 25" enters into this at all because I don't believe the engine you have is what is called a 25" engine in the Mopar world. Even if it does measure 25", I don't think it is related. I could be wrong about that, and I hope someone will correct me if I am. I can see all the way from here that the engine is quite different than what I would expect a 25" engine to look like.

 

The commonly referenced 23" and 25" engines are basically the same thing. They are so similar that people are often advised to measure the cylinder head to see which they have. 23" was often Dodge/Plymouth and 25" was often Chrysler/Desoto. There are exceptions. In Canada, 25" engines were debored/destroked and substituted directly for 23" engines in production. I suspect there is at most, 2" difference and everything else almost fits. None of that helps you at all.

 

If I were you, I would study how that 23" engine was mounted originally and copy that. It sounds like the location of the pedals etc. is going to cast the rear mount positions more or less in stone. If you have an extra 5" in front, that is actually a good thing. I don't know what those newer mounts look like, but I suspect you need to make a crossmember, and 5" is plenty of room for one. That is way more stout than individual mounts. With all that room you can probably run a brace forward and tie it down to the spot the old engine mounted to, wherever that was. I'm just speculating though since I haven't seen it.

 

You can probably get a starter for that engine that will work with the button if you want to.

 

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The engine in the car predates the 23"/25" distinction, note that the distributor is on top indicating a first generation Mopar engine. With its waterpump outlet pointing to the right it is similar to the last two versions of the smaller 7-bearing sixes that Chrysler made up to 1930 (Series 60-62-65-66), more precisely a Series 65 or Series 66. By the way, that rather unique waterpump might be worth a good chunk of your gas money going to Oregon. Enclosed a picture of my Series 65 engine with a yardstick illustrating its 24 3/4" head.

 

29Chry230227-ToppenpeinS65er2475tommarlangkopi.jpg.6ba575544976bf06b64986b8a3a46421.jpg

 

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  • 4 weeks later...

I revisited this aging thread because, as I progress through the labyrinth of installing a 23”, 1951 Dodge Pickup engine to replace the 25” six cylinder flathead presently in my newly acquired 1929 Fargo express, I am learning how very absurd the continual citing of these measurements are when deciding to do a engine exchange.

The measurements are given in allusion to the “length” of the engines, but actually are taken by the length of only the cylinder heads.
The real consideration is the width of the rear engine mounts…..the old engine is a good 4” wider than the replacement engine, and, while the width of the front engine mounts are identical on both engines, those on the old engine are at least 7” further ahead of those on the new engine. This is of some concern in the increased distance between the radiator and the fan and the expansive space now open between the radiator housing and engine front….greater space, less air movement…..less cooling.

Placement of the pedals on the bell housing of the new engine raises a lot of questions regarding placement of the pedals (which I don’t have) on the old engine.

I had a breath of relief when I found that the 1951 Dodge engine uses a master cylinder similar to the one used with the Fargo engine, mounted ahead of the brake pedal, and uses a pedal mounted clevis to push the operating rod forward. Unlike the master cylinder mounted into the frame of my 1951 Plymouth, with a nearly identical six cylinder flathead, and also uses a pedal mounted clevis, but it uses a bell crank to reverse the direction of the operating rod. There was no small amount of relief felt when I took measurements and found that my pedal problems may be eased by bending the clutch pedal mounting pedestal about 7” to the right….to clear the left side of the cowl, and add some length to the master cylinder operating rod as it pivots on the brake pedal clevis.

The 25” measurement of the cylinder head, as compared to the 23”  measurement really becomes insignificant when it is considered that these numbers are lost in the difference in spacing of the brake and Clutch pedals due to pressure plate and bell housing differences in size, and the spacing differences caused by the engine mounts being built into the front of the 1929 engine, and are spaced a greater distance from the block because they are integral to the cast iron timing case.

I could go on here for hours, and I could post a thousand photographs to explain what words won’t describe, but I will close this epilogue with the advisory that you seriously consider whether or not, at the instant the replacement flathead six cylinder starts, you will have one iota of doubt as to whether you SHOULD have gone with that 289, 318, 283 or 440 magnum.

This is the time you need to plan to install the V-8, and console yourself as a virgin install, and not the coupling of a failed marriage to a much ridden horse.

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Edited by Jack Bennett (see edit history)
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On 12/16/2023 at 4:40 PM, Bloo said:

I don't think 23" vs 25" enters into this at all because I don't believe the engine you have is what is called a 25" engine in the Mopar world. Even if it does measure 25", I don't think it is related. I could be wrong about that, and I hope someone will correct me if I am. I can see all the way from here that the engine is quite different than what I would expect a 25" engine to look like.

 

The commonly referenced 23" and 25" engines are basically the same thing. They are so similar that people are often advised to measure the cylinder head to see which they have. 23" was often Dodge/Plymouth and 25" was often Chrysler/Desoto. There are exceptions. In Canada, 25" engines were debored/destroked and substituted directly for 23" engines in production. I suspect there is at most, 2" difference and everything else almost fits. None of that helps you at all.

 

If I were you, I would study how that 23" engine was mounted originally and copy that. It sounds like the location of the pedals etc. is going to cast the rear mount positions more or less in stone. If you have an extra 5" in front, that is actually a good thing. I don't know what those newer mounts look like, but I suspect you need to make a crossmember, and 5" is plenty of room for one. That is way more stout than individual mounts. With all that room you can probably run a brace forward and tie it down to the spot the old engine mounted to, wherever that was. I'm just speculating though since I haven't seen it.

 

You can probably get a starter for that engine that will work with the button if you want to.

 

It’s getting late, I’m rather tired, and I won’t be posting reams of photographs.

But, I will say that the Fargo has a sheet steel floor to the bed which is probably over 1/8” thick and weighs at least a couple hundred pounds.

I have the tongue and groove lumber already, and have stripped the wood of the rear of the truck down to the frame. This will be used to replace the rotten wood in the bed.

Since the truck will never be returned to commercial service, I see no need to clean the sheet of steel, and replace the bed floor using it.

Considering this, I find myself the unexpected owner of a sheet of steel, pitted and rusty on one side, but decent and useable on the other.

So, I am considering making a steel belly pan frost the truck, extending from the left to the right frame, duplicating the front motor mounts built into the existing frame cross member, and cutting panels to replace the lower part of the new engine exposed because it is narrower, and shorter than the original engine.

I sure wish I had a plasma cutter, but buying one for a single use would be dumb. So, I think I’ll just use the zip tool and MAP torch to cut and shape this thing.

The clutch pedal mounted on the 1951 engine would work perfectly with the firewall cutouts, the drop of the steering column and the present brake pedal position. That is, if its pedestal was bent about 7” to the engine rears right. If I can make a decent bend in the pedestal which moves the clutch pedal about 7”, I.ll be one happy puppy.

Comments, suggestions, advice, admonishments, criticism or whatever may be productive is welcome.

Edited by Jack Bennett (see edit history)
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