The factory 15x7" rims have 4.25" BS - and work fine with many tire sizes.
A 15x8" rim would need 4.75"BS to put the wheel and tire in the same space.
Bottom line, it's a combination of wheel diameter and width combined with the tire diameter and width that will determine if the combo will work.
I run 235/60/15's front and 255/60/15's rear on 15x7's with 4.25"BS on my '64.
Your results may vary...
