Wow...tons of ideas here, Smokey Yunick would be proud! (I also think I'm in way over my head here, so please bear with me)

Motor is a 218, transmission & clutch are stock. Gear ratio is stock factory cataloged 3.73 (I have the option of running 3.9 and 4.1, as those were factory options)

Flywheel must be a stock cataloged item for year/model/type of car, so a 230 flywheel is out. Rules specify that the flywheel cannot be altered in any way. Vehicle must also be self-starting.

Rules say; "Carburetor must be listed for make and model car but jets may be of any size". I'm interested in the possibility of honing it, as I believe this would be a 'gray area,' but honestly wouldn't know where to start.

Air cleaner must be stock as well.

The rules do not address pistons per-se...it simply says "complete motors must be in chassis and body for which they are cataloged." That being said, I inclined to think that some modifications would be allowed (unless otherwise specified, as in the case of the camshaft & flywheel), provided that the parts are properly cataloged factory parts and retain factory appearance - The April 1951 issue of Speed Age details the fact that Johnny Mantz's 'Southern 500' winning Plymouth was outfitted with Grant piston rings and Smokey Yunick recalled watching a young Richard Petty polishing the ports on 'papa' Lee's flathead. George Asche tells me that one of Cotton Owens' flathead speed tricks was to deck the block 0.040", so some modifications of the factory parts was allowed (or overlooked). I suspect that pistons would have been stock or stock replacement; I do not know if 'high performance' aftermarket pistons were produced during this period, although lightening stockers may have been standard operating procedure. Ditto on the rods.

Rules for valves & valvetrain simply says 'stock'...I'm sure any modifications would have been limited to a performance-oriented valve job, maybe shimming the springs as you suggest. I know next to nothing about valve jobs/reshaping, so I might need to do a bit of reading to fully understand the valve modifications you suggest.

Rules say nothing about the oiling system, so I don't see why a baffle/windage tray/scraper would not be permitted. Here again, I have limited experience with these type of modifications, so I'm open to suggestions.

NASCAR rules were pretty strange in the early days...it is pretty common knowledge among folks that were 'there' that NASCAR DQ'ed some drivers for minor 'gray area' infringements, while others were able to get by with blatantly illegal modifications. There is still much controversy over whether or not Lee Petty used an illegal camshaft in his '49 Plymouth during the 50-51 seasons.

I guess my bottom line is to recreate as faithfully as possible the low-budget 'thrill' of early stock car racing. I've gone to great lengths to insure that the suspension/body/interior of the car is 100% period correct, conforms to rulebook specifications, and matches extant originals and period photographs - so I'd like to do the same with the drivetrain. I'm not looking for super-high HP numbers, as it would simply not be consistent with the historical record...the fastest qualifying speed recorded by a Plymouth in 1951 was a 'blazing' 81.09 mph...but I'd like to build it to be somewhat on the conservative side of the 'gray area' as far as internal modifications go. Hope that helps give some insight into how I'm approaching this.

Thanks again for your time...any guidance is appreciated!

Gary