I'm using a '78 Camaro rear end which should be the same width as your '81 rear end. Wheels are 15 x 7 wheels with a 4.25 backset. Tires are 205/75R15. The tires have rubbed just slightly on the box side - made marks but didn't rub the paint off - this would have happened under hard cornering. Therefore, to use wider tires than I have, you would have to decrease the backset to widen the track.
