The GMC six cylinder engines are not uniquely military. It is the bolt on parts that make it different. The Hydromatic transmission is the same bolt pattern as civilian units. There were many combinations of transmissions that GMC used in their medium duty truck lines. In the mid 50's, GMC used at first an Oldsmobile 324 V8 as well as 270 in line 6's. Later they shifted from the Olds to a Pontiac 336 V8 due to premature timing chain failure with the Oldsmobile engine. While the bell housing bolt pattern is the same (even on the Cadillac) and there were both 4 and 5 speed manual truck transmissions that will bolt up, (there were even dual clutch setups) the problem with a conversion to stick shift is the lo range feature in the M211 Hydromatic transmission. A complete swap would require a change from the in and out transfer box of the M211 to a two speed transfer case such as used in the CCKW. That being said, I have seen several swaps that work well using the in and out box with a stick shift and operating in only what could be described as high range. Our own M220 only gets operated in low range in reverse to avoid the potential damage to the transmission that seems to be an inherent problem with this transmission. We never haul a load that would require that low gearing.
Crank is machined for pilot bushing or converter guide (same same.)