Tom, if you are asking if it would ever be appropriate to run 17-inch tires on a history GT40, the answer is no.
Well, for street cars in the 21st century, it's fine. But 17-inch tires are a relatively new invention, and for the first 30 years of a real GT40s life (at least!) it would only have run various 15-inch sizes, depending on if it was an early or late car, wire wheels, Gulf flares, etc. etc.
I can't imagine anybody ever putting anything other than 15-inch wheels on a genuine GT40, ever. But lots of replicas use them to good effect, because you can get better tires for them (or at least, you could--the supply of 17-inch tires may be drying up sooner than you think!) :cry: