GMC didn't use "tons" in technical documents, only in sales documents like the one below. Given that 250 models are considered 1 ton and the document shows the 300 model as 1.5 tons I guess your 280 model would be considered 1.25 tons.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
