The Stovebolt Site Forums The Shop Area Engine Shop Flywheel, from hell.... and starter issue 47 1 ton, ~1960 engine

All 1941-62 flywheels use the same mounting pattern.
I have not been following this thread, but in scanning it it sounds like originally it was starting fine with no growling noise. That would not happen it there was a mismatch of 6 and 12 volt parts.
It sounds like both the flywheel and starter are 12 volt in this case.
This may have nothing to do with the growling noise, just the "not fully engaging" problem, but there are two 12 volt starter drives I have seen that look the same except one has a much longer gear. There is a possibility the wrong drive was used.
You need to actuate the lever and see if the drive teeth come back all the way to the end of the shaft and housing.