EmTee

Well, owning a '67 myself helps quite a bit...

There should be a plunger type switch somewhere on the emergency brake pedal assembly.

Well, it is "The Sportwagon from Hell" after all!

Do you have a test light or Ohm meter? You should test the rheostat winding for end-to-end continuity. Use an Ohm meter to check across the winding, or apply 12V to one end and touch a grounded test light to the winding and verify the light is lit. If it does not light, probe the winding closer to the grounded end. There could be a break in the rheostat winding.

When in doubt, I use a battery hydrometer to check the electrolyte.

'67 seat backs have locks to hold them in place. The button on the side must be pushed to fold the seat back forward. If you modify the bumpers as Joe P. suggested, just make sure the latch still functions. Shaving the bumpers should be fine, if you shim them to straighten the seat back, then some latch adjustment may be needed.

That's always the first thing to check and correct if necessary before further troubleshooting.

I use mine to check for equal brake adjustment at each wheel. When adjusted correctly the temps for wheels on the same axle are within ~5° F.

Ah - I saw it was 400+ pages long and ASSumed it was the shop manual... The link you posted looks like the least expensive option. I prefer the books, but $200 is kinda pricey unless you're inclined to tackle pretty much all of your own maintenance and repairs. If so, the books will pay for themselves after a couple of big jobs. If you go with the soft copy you can just print the relevant pages and bring them to the garage.

...as well as the rheostat and the wiper. Put some contact cleaner or WD-40 on a piece of paper between the wiper and the coil and move the wiper over the coil. Check rheostat operation with an Ohm meter.

Unless they filled the hole on the inside of the lid you should be able to look from the inside and locate where the lock cylinder hole belongs.

If it's something to do with the pressure regulator, I suppose a risk is that the spring breaks and/or the piston frees up and pressure suddenly drops lower than normal.

For a temporary installation you may want to consider a sender that fits into the upper radiator hose. https://www.amazon.com/Dewhel-Aluminum-Temperature-Radiator-Adaptor/dp/B018FY12CW/ref=d_m_crc_dp_lf_d_t1_sccl_2_1/140-3825895-8753154?pd_rd_w=CejC4&content-id=amzn1.sym.76a0b561-a7b4-41dc-9467-a85a2fa27c1c&pf_rd_p=76a0b561-a7b4-41dc-9467-a85a2fa27c1c&pf_rd_r=2CSYCTKRMXS6YGHW7706&pd_rd_wg=1qmPv&pd_rd_r=ed78afd1-7c15-4d2d-92fd-ff5ee0417609&pd_rd_i=B018FY12CW&th=1

Olds 98 would probably be the same.

95 years of shock loading probably contributed. It sounds like it broke at a stress point created at the spline transition. You might try getting the good axle magnafluxed or dye tested in that area to see if there are any cracks already present. Consider looking for another one to keep on the shelf - just in case...

DO NOT rely on the jack alone, however! Put a pair of jack stands under the frame before going under the car.

About as cheap as I could find... https://www.manualslib.com/manual/230809/Buick-2002-Rendezvous.html No Reatta, unfortunately. Check Ebay (https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=1989+reatta+shop+manual&_sacat=6000&LH_TitleDesc=0&_odkw=reatta+shop+manual&_osacat=6000)

Porterhouse!

When I park my car in the garage after a drive and open the hood I can literally hear a 'fizzing' noise coming from the carburetor...

Fresh off the rollback!

Skylark?? No, definitely not. Pieces from a LeSabre, maybe... Is the whole roof really bad enough to justify complete replacement?

Maybe better to buy one of these for long trips...

I wonder whether the fuel in the bowl gets hot, starts to boil and then the float is no longer buoyant enough to close the needle valve. If so, then the engine floods. Even after stalling, fuel may be siphoned into the carburetor until the fuel cools down. I'd first check the float setting and the float itself. If those check out as OK, I might try installing a heat shield under the carburetor. If the fuel is boiling, I wonder whether adding a little kerosene (or diesel?) to the gas would raise the boiling point enough to help. The octane reduction shouldn't be a problem for this engine.

A 455 in a Catalina is unusual (even a convertible). Most would be in Bonnevilles (or later Grand Villes) too bad about the rust...

Now, THAT's what I'm talkin' about - I love the original 'wide-track' Pontiac!