what is the difference between a muncie 20, 21, 22? Is a t 10 better? and i have a th350 short shaft in a 80 z with a 406, if i get one of these will i need a new drive shaft? thatbk you.

 

the m22 is the strongest thats why it got nick named the rock crusher and you will probably need a different drive shaft

 

The M20 is a wide ratio, M21 is a close ratio, and the M22 is a Heavy Duty close ratio. The M22 has a low helix angle cut gear set that increases the strength. The late style T-10 is a very strong transmission and there are several gear sets available. They came in close and wide ratio styles with a somewhat better set up for the wide ratio model than the earlier muncie. There are two different output yokes available. The Muncie was available with both and the late T-10 was available only with the larger. This is being quite general because there are so many variations of each. Both early T-10's and early Muncies had small output yoke dimensions. Later configurations of each had the large output style. Input shaft changed in 1970 to fine spline on the Muncie. Late T10's have the fine spline input. It is always good to know what car the trans is from and the year. I hope that this helps.
Your drive shaft will work but you will probably need to change the front yoke to the larger style. The short TH350 and the Muncie use the same length drive shaft as does the T-10.