All muncies before a certain year (1970 I think) had 10 spline input shafts, m22's included. '70 and later all were 26 spline.
Ones older than a certain year ('68 I think) used nuts to secure the shift arms to threaded shafts sticking out of the side cover. Later years used bolts.
The length of the flat that engages the shift arm is longer on the "bolt on" types. You can use a "bolt on lever" on a "Nut" trans, but not the other way around.
"camaro" transmissions have the speedo drive on the passenger side. All others have it on the drivers side.
It's worth noting that the passenger side speedo drive was to clear the 67-68 crossmember mounted muncie shifter. If you're using an aftermarket hurst shifter and converting a former automatic car, a driver side speedo muncie is a boltin, and your existing speedo cable will screw right in.
All muncies used the same bellhousing bolt pattern and bolt size, the length, and the same transmission mount.
A muncie and it's bellhousing are the same length as either a powerglide or a T350, and will directly bolt in.
Many but not all muncies were "coded" (M20, M21, M22) by grooves cut into the input shaft, none, 1, or 2, though which is which escapes me.
