In that day, performance tires where rated with letters and then the aspect ratio. Such as G70-15.
In SoCal, for cheater tires, a lot of guy's used walnut embedded snow tires (still made), made with walnut infused soft rubber. DOT was created in '67 and by '71/'72, race tires weren't policed. I ran Stock Car tires, on 10" wheels, on the back of my K-code Mustang and never got stopped.
There were still recaps back then and I vaguely remember 2 groove "Cheaters" but, not sure of the date.