Identifying the series of GM 12 bolt rear end...?

[Chrisw]

Https://ibb.co/3R4bY8D

*wont let me imbed the photo for some reason*

So I finally got mine and pulled it apart. Gearing is a 4.56 so I'm assuming this makes it a 4 series. If my measurements are correct, its 1.82 from the flange to the end of the bearing.

It clearly has a large shim on the flange... to allow it to take a series three gear set I assume... although it brings it to about 2.02... which seems to be a hit heavy. My measurements might not be perfect though as I'm eyeballing that one.