The 8.25 axle I took out of a '75 four door Valiant was 3/4" narrower flange to flange than the stock 7.25 axle in my '65 Barracuda. If you can get the 8.25 from an A body you wont have to move the spring perches. With a Mopar offset spring hanger kit and cop car spec rims (15x7 with 4.25 backspace) I was able to get 245-60 x 15 tire in the stock wheel well with no other mods other than moving in the spring perches a bit. Plenty of clearance all around, enough so that I think you could get a 255 tire in there without any rubbing. Of course they are all big bolt pattern so your stuck with that issue (rims, front brakes/spindle).
