I have a '65 Chevelle that I'm restoring. I'm trying to switch from a single spin to a posi that I got from a '68 Camaro axle. I can't switch the whole axle because of the leaf spring/coil spring mounts etc. I have a 10 bolt in the Chevelle with 3.08 gears and has 3/8" ring gear bolts. The Camaro axle is a 10 bolt with 3.07 gears and 7/16" left hand threaded bolts. The two differentials seem quite alike, but the small differences are troubling me. The pinions are different in bearing sizes so I can't switch everything from the Camaro to Chevelle, so I tried using the ring gear from the Chevelle on the posi diff. because the carriers are pretty much the same, but then my pinion and ring gear barely make contact. It's almost like I need a 1/4" spacer between the ring and the carrier flange. There is nowhere else to shim, not even between the bearings and the axle housing. Using 3/8 bolts in place of the 7/16 bolts for the posi make me a little nervous, but I did make some sleeves to take up the play in the carrier flange bolt holes. I even tried using the original ring gear for the posi, but its outer diameter is too large and won't fit in the axle housing. Do I need a spacer between the carrier and ring? What else can I do besides buying a brand new posi?

If it were me, i would buy the posi.

I think that your 65 rear is a 8.2 the 68 is a 8.5 ???? I think??
They do not interchange. Buy the Posi !!!

Sounds like you have one 8.2" (with RH 3/8" bolts) and one 8.5" (left hand) but a 68 wouldn't have come that way--maybe it was swapped during it's lifetime? Compare the photos and see if you can tell if it's an 8.5" from the Camaro (photos borrowed from Nova sites)

http://www.novaresource.org/images/rears.jpg

Both rears,if they are 10 bolts from a 65 Chevelle and a 68 Camaro..should have an 8.2" diameter ring gear and everything internally should interchange.Sounds like the Camaro rear is later than 68...like something from the mid 70's which would be an 8.5" diameter ring gear.