Im running 235/75R15s on my 63 , which is a little narrower but taller, with no modification
A 235/75R15 is a lot narrower and not as tall as the 33x12.50R15. Here are the spec.'s
235/75 R15Section width is 9.4 inches
Height is 28.9
33x12.50R15Section width is 12.4 inches
Height is 32.7"
On my short step I am running 33x12.50R15 on the rear but I widened the bed 4", check out my build thread below, See post #12.