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.