Previous generation, in fact: 1947-55 Chevrolet Advanced-Design / GMC New Design. With the 1947-53 angled bed rail and the 1951+ vent windows, so a 1951-53 model.
No front view, so impossible to say which of the 2 makes it is.
_____

Edit: due to the single vertical reinforcement bar on the bed side, a ½-ton Advance-Design 3100 / New Design 100.