I think Don is right on most of the rules, and a few others have mentiooned it too. On top of tires, you need a good weight rule, the top cars can easily bolt on weight. If you upped the weight rule you could get back some of the iron block engines( the ones sitting in barns and garages). But with this im sure that someone will say that they will not have the same performance, and ill agree with that to a certain extent, but if you were to mandate a tire co. and use the Hardest tire made for a midget, the top of the line engines may not hook up