Here is some more specific information. I am terribly confused with the 8.2 and 8.5 differences and the identification of the mystery posi carrier. I am looking for the most affordable and practical way to upgrade to a posi rear end. I also have the 8.5 rear end that I could potentially use as well. I would prefer to keep the original rear end under the bird just to keep from relocating the leaf perches but I am open to suggestions.

NOTE: All images have captions to explain details.

Here is my rear end that I pulled out of my 1967 Firebird 400.


Here is the date code and number on the housing.


Here is the two letter code. "XC"


This is my open carrier (left) next to the first posi carrier. The carriers appear identical in overall height but the ring gear sits noticeable higher on the posi unit. I could not find any part numbers on that unit.


Then I compared my open carrier to another style posi. The carrier in the middle also seems to be identical in overall height and the ring gear mount seems to be a perfect match. However, that carrier is a 410408N, which decoded to an 8.5.