With a gvw of 4800 and 6 lug wheels, it has to be 1/2 ton. GMC, unlike Chevy, had long bed 1/2 ton in the first series. The curb weight of the truck should be about 3800. If it were a 3/4 ton the gvw would be about 5600, and it would have 8 lug wheels. For the engine size, check the serial number stamped on the boss just aft of the distributor. The first three numbers should be the displacement, 270, 248, 228 or whatever.
