8 3/4 rear 741 / 742 center case question - HELP!
My observations so take them for what they are worth.
The pinion thickness/bearing size is a red herring. They all have the same neck down in the weakest area... where the yoke attaches.
The 742 has a real bad stress riser in the pinion, IIRC. the 489 also has a 90* stress riser, the 741 has no stress riser.
The 489 preload crush sleeve is a POS. Anybody building one that wants it to last should replace the sleeve with a solid spacer.
Broken gear teeth is a bigger issue than anything to do with pinion bearing size. More of a cap issue.
741's are plenty tough. I've had 426 Hemi and 440-6 cars with 741 SG's in them.
Pull the sure grip from the 742 case and put it in the 741 case. First , check backlash first on 741, then reset to that reading with sure grip installed.
Too bad you are in Australia. I'd be interested in the 3.91's from the 742 case.