As I recall, J C Whitney used to sell whitewall paint. It was a "specially blended" latex paint. My grandad told me about painting white walls back in the 30"s.
I painted some radials on my 56 chevy back in the 80's and it looked great. I used some good ole latex house paint. Yup, it looked good till I drove it and the natural flexing of the side walls on the radial popped the paint up.
It would work on bias ply, as the sides don't flex, but not so good on radials. Maybe some "special blended " formula would work on radials as well!
