I'm not an expert at this, but here goes. The width of the tubing and maybe the thickness is the issue. Read the USAC rule book and it will tell you what it should be. There also may be references to older cars in the rules. You would be crazy these days to run those cars outdoors. It could be potentially dangerous indoors also, IMO. Racers have been fatally injured at the Tulsa Expo Center and the Speedrome which are very small tracks.