My restroation interest is all M series post WWII vehicles. Willys and Dodge. I havent had any interest in owning a WWII vehicle because I consider them "Too primative" for use as a regular vehicle. I drive mine alot so they get used in the desert, filmed reinactments parades etc. WWII stuff just isnt that useful as a daily driver.
That being said, Ive been in the hobby awhile and heard these stories. When I read about the goose motors being from surplus trucks, I figured out quickly that they werent CCKW motors as those were 270ci.
Ive heard that they might have been half track motors and that too I dismiss as White was the contractor for the M2/M3 and IH for the M9. They didnt use GMC motors at all to my knolwege. But, I am not an expert.
I can referance a friend that has two halftracks and pick his brain. I know that he got a NOS (Thats New Old Stock) half track motor in a crate up in Washington a few years back. He spent a ton of money just to get it, just to have it.