About the markings ...
Does it have any stamped metal tags on the dash or map compartment/glove box door? If not, how do you know it was a military truck? If it was, it should have some sort of a tag on it to say so. And about the markings -- it would depend on which service had it and what unit it was assigned to. Military trucks from all eras have a plethora of markings all relative to branch and unit down to the individual motor pool. Not all civilian/commercially sourced vehicles would be marked like the true tactical vehicles (i.e., with the white star on the door for the Army and white letting on the hood sides, or just orangish gold letters on the hood sides for Marine Corps trucks of that era). If it was an Army truck, it might have had some white lettering on the doors with words like
U.S. Army
(number)
For Official Use Only
Kinda like thisOr it might not have had anything at all, maybe just some motor pool specific markings on the bumper. Really hard to tell without knowing what branch and unit it was last assigned to.
Find those tags and tell us what they say (or show us a picture). If no tags, it might be impossible to know.
Good project, though!
And Welcome to Stovebolt!
John