I have 15" Ralley IIs on my '69 with no problem. (Had to use 15s because the half assed disc brakes I used didn't fit inside the 14s) The tire diameter is exactly the same as the 14s were.
I know that some 14" Rally IIs can work with some of the disc brack conversion kits. You do have to shave a bit off the caliper. I've seen it done with no issues. Perhaps if the brakes were employed more it might come up.
1968 400 Coupe, verdoro green, black vinyl top, auto 1969 GTO Judge coupe, Carousel Red, manual 1971 Trans Am, cameo white, auto 1970 Buick Skylark Custom Convertible 350-4(driver), Fire Red, white top, auto 1972 Buick GS Stage 1, Royal Blue, black vinyl top, auto
