John.....Sometime in the very early '70s, John Treder had the 12 bolt fitted to his A/S. A local shop used their "drag race bits" for the conversion. Aside from a pain to swap crown wheel & pinion, it performed flawlessly. Until we went from 5, to 6 litre engines (A Sedan to GT1). At the first National at Sears Point that year, the left rear was overtaxed by the hp/torque (586/525). The inner bearing race "became" part of the axle snout. A quick call to the original fabricator, & he said, "Bring it down." After one look at it, he stated, "You're still running that setup, I thought I contacted everyone & got them to upgrade to my stock car hubs & snouts!?!!?" I still remember the smell of burned 140 wt. Valvoline!