I have a Muncie that i have been trying to sell and dnt know whether its a M21 or an M22? The transmission has clearly been rebuilt sometime in its past for starters as there mismatched bolts and threads that have been tapped. there is a ring in the "fine spline" input shaft which says M21. It also has a fine spline output shaft. the casting numbrs are 3925661, the Date code numbers are P3(A/4)04, the tail shaft numbers are 3978764. there are also numbers stamped into the case around the date code 133021 and 13N133021. there is no Ratio letter after the date code.

Look a the pic's as see which gears you have
http://www.chevelles.com/forums/showthread.php?t=301063&highlight=M22+gearset
Look's like M21 to me.

I think you can safely say it is not a M-22 with the angle of those gears. It looks as though it is more likely an M21

hey thanks fork the help!

One ID ring designates it is an M21.........