For the paint, Testors Model Master Medium Green is a pretty good match for Marine Green during the Vietnam war era. For markings, they are pretty basic, on the sides of the hood would be a USMC and a serial number. There would also be a serial number on the front bumper and on rear panel. The markings would be in yellow. There may be more that were specific to your girlfriend's uncle's unit.
Actually, if he served in 1968, he might have actually been on an M35A1, M35A2 wasn't introduced till 69 and later. Visually, it had a different light set up; instead of the amber turn signals and large red brake light/turn signal combo, it had black-out lights in their place both front and rear. It also had a different muffler set-up. The muffler ran along the frame and exited between the right side rear wheels. Check here to see Gun Truck's build of Nancy, an M35A1 Guntruck. http://www.guntruck.com/Nancy.html
Here are USMC markings from Vietnam on an M35A1:
Not sure what all the streaks are, mud I guess.
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