Does anyone know if 255/50/16 toyo RA1s will fit on a 68 Cuda?
They will fit the rear with about 4.25 backspacing on a 8" wide rim. Or in the rear with 8" wide rim with 4.5 backspacing, but could need slight wheel spacer like 1/16" or 1/8".
If they fit the front, it will be with 16x8 with 5.0" backspacing. 4.5" backspacing on the 16x8 in front will definitely rub the front lower fender lip.
I have 245/50/15 on 15x8 rim with 4.5 backspacing on all four corners of my 68 Barracuda. It has the 73-76 big disk brake swap, 4 deg positve caster, 1 deg negative camber. The lesser caster the more the tire will move foward and toward the fender lip. It is very close up front on the front lower wheel lip. So close that your results will very car to car. Including the small changes from alignment settings. I little 1/2" x 3" tapered fender lip should fix any problems.