Al,
It seems as though it was once popular to transplant a 1941-45 GMC G-508 (CCKW) engine and transmission into the 1941-45 Chevy G-506. I think the compelling reason for the swap was that the Chevy babbit 235 engines bit the dust and the GMC 270 was always a insert bearing engine. Additionally, the Clark 5 speed transmission from the GMC gave the Chevy a little more top speed as it was an overdrive.
GMC CCKW's were always outfitted with a 270 from 1941-45. Chevy's were always outfitted with a babbit 235 from 1941-45.
I am not sure about the usage of diesels in WW2 military trucks/vehicles.
Paul
