Look at the wheels, she's a dually, meaning 1ton or better. Probably originally had a flat bed or some type utility bed, maybe a wrecker bed. The bed wouldve been aftermarket from some type of upfitter so records on type bed might be non existant. Unless you can find a previous registration that might list a classification. The emblem under the GMC badge on the back of the hood will signify the weight series, i.e. 3100, 3200, etc. It looks to have the larger back window which dates it in the 50's, the split windshield dates it around 51 or 52. 1953 and up on that body style had a solid windshield.