My camaro is a 95, 3800 series II, has an open diff. Embarassing one wheelie peelies. Occasionally spins two.

4th gen parts cars are hard to find, hoping to score a posi unit out of an older third gen car.

 

Only a posi from a 90-92 will work. Earlier versions are made for 26 spline axles. 90+ F-bodies use 28 spline axles.

You can also find one from a 90+ S10

 

Awesome! What is the cut off year for the S10s and what models had a posi?

 

You don't want anything from the S10. They got the Governor Lock, which has a lot of small parts in it that break easily. You will be much better off getting a 4th gen rear end. The 3rd gen used the Auburn, which isn't the best choice. They wear out quicker than others and can not be rebuilt. Look for a 4th gen with the Torsen diff, or get a new Eaton Posi. You will also need to get the right series for the gear ratio that you have. If you have a 3.08 to 2.41 then you will need a 2 series. If you have a 3.23 to 4.10 then you will need a 3 series.