Hmm, I was thinking they had drag slicks even in the mid 60's. Wasn't big daddy's swamp rat around in the late 50's?
I agree all the manufacturers used skinny tires because most everybody else used them, and they were main stream, and their " Win on Sunday, sell on Monday" marketing was working without using large wheel tubs, but this may have given any 1 of the big 3 a leg up.
I could see it affecting the trunk space a little, but on the A body cars and full frame vehicles, you could fit like 6 people in the trunk! I think they could sacrificed a some trunk space on those cars at least. A redesign of the rear seat would have made it work without sacrificing hip room. Nix a couple of extra ashtrays in the rear and its paid for...
I think it was do-able back then. I think the design of the cars was great across all the manufactures really. When you see some of the prototypes they were looking at and the other possible names of the cars, things could have turned out a lot worse. I think a possible name for the Camaro was the "Chetah" ...