In WWII, there were so many different vehicles from so many manufactureres the parts supply chain was a logistical nightmare.
This brought about the "M series" designation in 1950. Everything would conform to 24v DC - ground with like components that would cross from one vehicle to another.
Example, In my 1954 willys M38a1 jeep, my generator shorted out last month. so I used a retro fit cable, and dropped in an alternator out of a 1975 M151 mutt.
In my 1965 Dodge M37 power wagon comm truck, I needed more power to run the radios and could not find the orignal 1960s 100 amp generator kit, so I dropped a 150 amp alternator out of a HMMWV into it.
Standardization is absolutly wonderfull. HMMWVs run the same headlight bulbs as my old jeep and that is what we still put in our old stuff.
As for the montage of WWII stuff and motors, I am 100% sure that the GMC 361 was not from a CCKW or a half track.
It may have benn used in other equipment other than trailer mounted eqipment. Like cranes, buldozers, who knows.
Its possible, that it may just have come from a civilian type vehicle that the military bought and used state side and then surplused the spare motors after the war. There was lots of vehicles like busses, cargo trucks and cars that were taken and painted green and used on bases state side that were not tactical vehicles or deployed overseas.