Welcome and gorgeous car. As Matt eluded to I'm the 38-80C "expert" (as evidenced by my forum handle) and keep a registry of the 20-25 or so know to exist. Yours is one I did NOT know existed previously. Right hand drive and possible McLaughlin would make it very very unique and rare.
As for the proportion some IS in fact not quite right, but i cannot tell from the photos exactly the problem, however the sidemount spare is sitting much too high relative to the rest of the car. The side mount on a RM should NOT be higher than the belt-line/hood-side molding. It does look as though you have some gap between the rear of the fender and the running board, more than normal, BUT the running board at the back fender is considerably wrong. I suspect you do NOT have factory running boards.
After studying the photo a bit more I do believe your fender (passenger side at least) is correct for the car. The rear most section lines up correctly with the front door to cowl gap and the size and shape of the fender well is correct for a RM. All else proportionally looks correct for the fender, though my comments on the side mount itself stand.
Whatever measurements, dimensions, photos, parts assistance, etc, etc, you need please simply let me know . I will PM you my contact info. I want you know that anything RM or worse yet 80C specific is rare and probably has to be made from scratch.
Of note other non-authentic or at least shall we say non US 80C things I see
1. rear Buick emblem is off a '35 or so. The correct one can be purchased here: https://www.ebay.com/itm/1938-Buick-Roadmaster-models-80C-87-Trunk-script-ornament-emblem/301058544580?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 note however it is missing the mounting studs. These are rare as they only fit about 900 cars ( total production of 80C and 87 series Buicks for the year). I have never seen a creased (that's the difference due to the crease in the deck lid) one with McLaughlin Buick on it, but i have seen non creased versions with McLaughlin Buick, so one would think it may exist.
2. The "B-post" window divider is either missing pieces or entirely incorrect as there seems to be a large bump out on the bottom that isnt on the US models and the top is missing the connection "spar" (I'm sure there is a more proper term) to connect the post to the top via a butterfly screw/bolt thing (that is reproduced). As noted they should be chrome but only the middle section, the outer section of the outer side is painted as is the inner side.
3. The wheels could be McLaughlin specific? the gaps in the rear ones in particular catch the eye as not like the US car. Are they 6 bolt? I know that McLaughlin Buick Specials of the same year had 6 bolt wheels compared to the US 5 bolt.
4. You're missing the rope on the back of the seat. These are EXCEEDINGLY rare as i am looking for one for my Model 87 and the mounting hardware is RM only ( possibly Limited too). You and I may have to have a set cast each from molds of my existing hardware. The chain itself between the hardware is of course nothing special and covered in leather. Hard to see but you may also be missing the foot rest which should be the same for all series for 38 with only the rod in between a different width. thus easy to repro.
5. The dash and steering is missing a few items, but none that i see are particularly rare or not produced.
6. Finally something is a bit off on your convertible top bow( the thin one visible in the one photo) the irons seem to be correct, this bow however seems to be in the wrong location or something is just not right
Overall the car looks very complete in general and i look forward to seeing the progress on it.
Some comments on what others have said. No disrespect to the commenters just clarifying items
Walt G's comments:
1. the face plates for the side mounts seem to be fine. RM's don't have the emblem like the smaller series cause the side mounts sit down far into the wheel well so you wouldn't see them. Aside from the whole assembly being a bit too high i see no issues with the covers.
2. Wood grain dash is the most commonly accepted correct finish ( in Mahogany for RM) , but there was a chevron pattern with a gold-ish tinted painted finish that is quite handsome on a 80C. I believe my 80C had this dash originally but it cannot be reproduced and thus i went with wood grain. Walt's point about white painted being incorrect stands.
1. That 80C you pulled actually had an issue with it's side mount covers as they were missing when a recent owner bought it at Hershey a few years back. Just FYI when doing a direct comparison as i never found out exactly what he did to get correct faces (appears he may have cut down small series ones as the badge should not be on the side-mount face. The rest of the car however is very well restored as i spent considerable time inspecting it at Hershey in the car corral. The gentlemen who bought it at Hershey couldn't get it running to his satisfaction lost interests and sold the car.
8E45E: well said. there are some considerable differences between McLaughlin and US Buick for 38 though not copious. HOWEVER supposedly all 80C bodies were Flint produced. Chassis are another story. I agree this most likely is a McLaughlin Buick despite going to India, still a "British Empire" country thus probably came out of Canada.