12 Bolt Ring and Pinion

[L78steve]

I've come across a 12 Bolt Ring And Pinion with a tooth count of 42-13. Would this be a truck 3.23? Came from an Olds GMC dealer.
All I have of the part number is 83729. Numbers prior to are torn off.

[Zman1969]

Olds made some 12 bolts that were different/less desirable than Chevy 12 bolts the posi's looked like 8.5's with a S shaped spring. with that said this may be what they are for, just putting this out there

[L78steve]

Olds had 12 bolt rears but had 10 bolt ring gears installed.

[Zman1969]

then I'd compare the pinion to a car 12 bolt, the truck pinion is thinner and weaker and a 8.5 10 bolt is larger-use same bearings as car 12 bolt so truck 10 bolts are weaker than the car 12 bolts and 8.5 10 bolts