Factory rims were 5.5". with a 6.70-15 tire as base equipment. That works out to a 215/75/15 in a modern radial. You could get away with a 225/75/15 on that rim, 235/75 would be pushing it for stability. As far a max size, I've fit 32x11.50x15s on them without any trouble. Might be able to squeeze a 33x12.50, but that might get tight in the rear fenderwells. You will need a wider rim for those, at least an 8" for the 11.50s, 10" for the 12.50s.
