Sorry if this is an age-old question, but I'm still new to the forum. Just bought a 70 Z and it has the Firestone bias-ply tire with the 60 in the oval. I see references where people say the Goodyear is "the" correct tire for a 70. Is it a fact that the 70 only came from the factory with the GY? If so, and you're interested in correctness and you're willing to deal with the inherent issues with a non-radial, why put the Firestone on your car?