not sure with the 255 but the same wheel ,rearend, combo on my 74 duster clears 245's great, when there gone i'm going with 255's i don't think you would have a prob unless car has been lowered8)
I've got 275x55-17's on 17x8 American Racing wheels with a 4.5" BackSpace, and had to use a 3/16" spacer to clear the spring shackles. Mine miss the fenderwell bu about 1/2", and the spring shackle by 1/4", so you should be fine.