Well I ran a 489 case with a spool 4.88 gears in a 8 3/4 in a 71 Scamp for 4 seasons and never broke it. Car ran 6.30’s would 60’ in the 1.35-1.40 with 4500 converter and trans brake. Ran 29.5 11.5x 15. It would hook so hard the housing dented the shocks from axle wrap. Had to use adjustable snubber to prevent that. Also had 002/003 SS springs. Guess I was just lucky eh?