The transmission should bolt up to the bell housing with no issues. A Chevy bell housing will not bolt up to a Pontiac engine and visa versa. The standards were pretty much interchangeable back then. The only issue will be to get the right spline and pilot bearing for the clutch and crank up front and the correct yolk and drive shaft length for the back.
The rock crushers were called that because they were noisy due to the straight cut gears. The straight cuts were supposed to be stronger.
The m-22 is easy to work on. I rebuilt a few back in the day.
The BW transmissions were not bad either but everyone wanted a Muncie
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