Just looked at a lot of photos of Chevrolet step vans from 1948 through 1968. None of them have a grille anything like yours. They started out with a 5-bar grille, went to a 4-bar, and then in 1968 went to a form of the '68 Chevrolet truck grille with one bar through the middle. Tlhis doesn't mean much because whoever built the body may have only used the Chevy chassis and running gear and manufactured the entire body as opposed to buying a chassis and front clip and completing the truck. Sorry I can't help. If you ever learn the year and body manufacturer let us know, please.
