[Allen]

Hi! I'm new to posting on this board, but have enjoyed reading it over the past few months.

Regarding your Muncie question, I believe that there are a couple of ways to determine whether or not you have an M20, M21, or M22.

I don't know what year GM started doing this, but after the date code on the side of the case there might be a letter A, B, or C. This letter indicates which it is. A=M20; B=M21, C=M22.

Another method might be to count the grooves on the input shaft.
Two grooves = M20; One groove = M21, Zero Grooves = M22.

I might be wrong, or backwards in my assumptions for what the groove or letter equates to. If so, I apologize, and I'm sure another person will steer us both in the right direction.

Good luck!