I think it'd be great for all the cars in HMC to be on 15" wheels with Goodyear Bluestreak cross-ply tyres. It'd be period correct, and the cars would look great, and slip and slide as they should do. This is what the Historic Trans-Am cars run on, and those cars look fantastic. Check them out here: http://www.historictransam.com/

The biggest issue with the Bluestreaks is the cost. That being said, by comparison to what people spend on other areas of a race car, they're a fairly minor outlay. But from speaking to people who race regularly on them, they are a lot of fun, and you should be able to get 3-4 events from a set. They tend to run out of grip before they run out of rubber, so you could say they become more enjoyable the older they get!