According to GMC parts books, the 248 was first offered in AD trucks and the same with the vacuum 2 speed. This does not mean that GMC did not use them in trucks built for the military. Much new technology came about during the war, and was offered in civilian equipment after the war. I think it is very possible that it was a truck built for the military to military specs during the war. Even later this was still done. I have a 1955 424 Series which is basically a 2 ton cab and fenders on a 3 ton chassis. This truck was sold to the military only and is not listed in civilian parts book