Looking for new parts for a 8.3 olds rearend. Also
a posi unit.

 

There's no such thing as an "8.3". What is the year and model? The 1957-64 full size cars used a 9.3" with drop out center section like a Ford 9". The 66-up full size cars used a 9.3" Type O axle that is completely different. The 1964-67 cars used an 8.2" BOP axle.

 

What make model and year is the car...MAybe that can help us. Jim