wtb a sure grip

To me pinion size is the most important. Therefore if you choose an 8 3/4 best choice is a #742 case. Second best choice in an 8 3/4 would be the #489 case. The Dana 60 is stronger, but typically much more pricey. Mopar installed these in hipo big block and Hemi 4 spd cars only because of the shock loads in dumping the clutch at a high RPM from a standing start. All others got an 8 3/4 as mentioned above in other postings. The best Posi units are the clutch type, manufactured by Dana and used until 1969 approx. After that Mopar switched to a cone type built by Borg-Warner. While horsepower is always a factor in parts longevity, driving style/use matters more. Either type rear/posi will live well behind an automatic, generally speaking, because a typical converter allows slip which decreases the shock load to the driveline on a typical launch from a starting line or traffic light. I raced a small pinion #741 case 8 3/4 (considered by many to be to weak for heavy abuse) behind a max wedge style built 440 (12.50 ET street trim/11.60's on slicks) for many seasons without any issues.