The rear end is a disc rear from an '85-'88 IROC. It isn't the original rear though because the case had yellow chalk on it that said '3.23 posi', so the RPO code off the donor car won't help me. It is a 10 bolt, and the ring gear(the big one) has 13:42 stamped on it. I know the chalk says 3.23, but the 13:42 thing is what's making me wonder. It for sure runs better than with my 2.73's. Any ideas? Oh it runs 2000rpm at 57mph in O/D

 

3:23