In the Pacific Northwest, many people race with SOVREN, the Society of Vintage Racing Enthusiasts (www.sovren.org). Picking the best Corvette for their race series would require a study of their rules, and also period FIA rules which can apply as well or instead. In essence, you're choosing between Corvettes built up to 1962, which are in the Vintage group, and then from 1962 to 1969, which are in the Historic group. You can use a '70 car if its design continued unchanged from 1969, but it has to comply with '69 specs. There were no pre-'62 Corvettes in sight last summer, which suggests they're not that competitive. The Vintage Sports Car drivers' Association (www.vscda.org) is another such organization with different rules.
To some extent, preparing the car is kept from being madly expensive because you can only use mostly period-correct parts. You can't have titanium, Heim-jointed, inboard-suspended A-arms; you can only have stock steel Chevrolet pressings. You can, however, use an aluminum cylinder block and heads because they were FIA-approved and used when the cars were raced new. Eric runs an aluminum ZL-1 big-block engine, and says it balances the car beautifully. However, he also says that the iron block is stiffer and can be more powerful, and that several other drivers have achieved a very similar weight balance even with an iron engine, so an aluminum big-block is not a guaranteed winner.
Cheating is rewarded by a DNC notice (Does Not Comply), which says publicly that you've been cheating. Repeated significant cheating gets you sent home. However, it's fair to say that most people have their own creative ways of massaging several of the rules up to a point. For instance, you can't help noticing that many of the SOVREN race cars have rollcages that contribute substantially to torsional rigidity. Given the agricultural design of the earlier Corvette chassis, this change would be of considerable help in keeping the wheels parallel. Preparation also involves a cutoff switch, fire extinguisher, trim removal, harnesses, a fuel cell, firewalls, a tow cable attachment, a wired fuel cap and oil drain plug, and a paint job-these cars all look pretty good and are required to look good.
You can't add flares or chop the bodywork, and your tires should stay within the wheelwells. They also have to be vintage-style racing rubber, so although they're grippy, they're also bias-belted or cross-ply, and you're going to spend quite a lot of your racing time sliding gently sideways. The good thing is these tires start to let go progressively and relatively early, so the slides can be controlled. Seriously grip race tires hang on much longer, and then spit you off into the kitty litter much harder when centrifugal force finally overcomes the friction coefficient of the tires, or when somebody bumps you from the rear.