[Chevelle-list] M-21 or M-22

[Jww1945]

I have a '70 SS 454 coupe with a number matching engine.  I restored the car to origninal condition over the past couple of years.   The 4-speed transmission is not original but I am not sure if it is an M-21 or M-22.    Written on the transmission housing in black marker is "M-21 Large". Not sure if this means anything.  Would like to know if it is an M-21 or M-22.  How can I determine which it is?   Is there any difference in the housing of an M-21 and a M-22?  Or are there other ways to determine if the trans is an M-21 or M-22?   Thanks, [EMAIL PROTECTED]