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It varies based on rear tire diameter and rear gear ratio (and drive gear). Same ones are used in M21, M22, some TH350, etc. There should be charts out there on the 'net.
I'm not an expert on this but here is what I have been looking at as well. The drive gear on Muncie's should be either 7 or 8. You might be able to count the gear in the transmission. I have not done this yet, but that would be my first guess.