Every A body 8 3/4 rear (67-73) that I have messed with 3:91, 3:55, and 3:23 have all been 741 cases. My swinger came with a 340 4 speed and had a 741 3:23 posi factory (now a 489 3:91 by my choice) Excluding my buddies 67 383 4 speed GTS, that came with a 742 case. Have 2 rears in my garage...