I have 265/50/15's on the rear of my '73. They are 24.5 inches tall. I would have loved them to be 26 inches tall but, they do look good. The next size up, is 295/50/15. I was afraid to spend the money for them and have them not fit. The 265/50 fits really well. My wheels are 3.5 outside and 4.5 inside. By the way, my tires are Cooper Cobra's. I know that the different tire manufactures vary a little.
Didn't we just have this discussion in the thread below ? 255/60 (pretty much perfect @ 27" tall) 265/50 (lil short to suit me @ 24.5") 275/50, (also pretty much perfect, an inch shorter than the 255/60's) 295/50's may also fit, but you're definately going to have to stiffen the springs and massage the fender openings and need as deep a back space as you can get (4" for an 8" wheel)