I picked up an A body 72 8 1/4 with a 321 gear. I've read the break is with the 271 gear set between the cases with the 271 using the "good" case. I have a 271 B body 8 1/4 of which I gutted to use the 321 ring and pinion in. I was going to just swap carriers but I've found that the A body rear uses the smaller bearings and races so I just bolted the ring on the B body carrier. I didn't realize there was also a difference in bearing size even though the cases appear identical except for the width. surprisingly, the pinion bearing and the crush sleeves are the exact same lol. the FSM shows a wrench to adjust the side to side play for the carrier instead of the long tool that slides into the tube. just a tid bit of info to share. I still have all the adjustments to make before I'm able to claim victory.
