Years ago, when I was younger and even more ignorant, I broke my Firebird's rearend. A garage I used replaced it with a rearend that they said came from a salvage-yard Camaro. It's a 10 bolt, and it looks to me like it fits the leaf springs perfectly. I found two codes off the bottom front of the differential housing: on the passenger side, GM 51, and on the driver's side, 3894859NF.

Do these codes identify this rearend? If so, what is it? If not, where are the right codes? I didn't look on the tube for the ratio code yet.

OK, I figured it out at camaros.net and camaros.org. Dunno if anybody's interested, but the axel tube code--PA0629G2--translates to a 3.08 non-posi, 10-bolt rear end made on June 29 at the Chevy Gear & Axel plant, Shift 1. The differential cast cose--F23 7--means June 23, 1967.

Now I need to decide if I want to convert this rearend to posi or not. How does this rearend compare to a '67 Pontiac 10-bolt?

i believe the pontiac 8.2 rearend had different gears than the chevy. they also have a different # of splines on the input shaft of the pinion gear.
the only thing i can tell you is they were different (and when pontiac makes something different, they make it better).