Why not let people run what they have rather than having to buy more kit?
We've been running pre 94 vintage at Caldi for a few years and people have let the car define their motor limit (eg a 17.5 in a pb mustang, 10.5 in an rc10) It still comes down to driving ability and the mustang was faster over 5 minutes anyway, it's meant to be for fun after all!
I'd love to do a bit more vintage racing