GMC built an EC280 series from 1946 to early 1947 and an FC280 through 1953. My guess is that may be what you have. The 280 series were sometimes called 1 ton specials, 1 1/4 ton and sometimes 1 1/2 specials. They were very popular in small school buses of that period. Most of them had dual wheels. Some were 18" and some were 20". Many years ago I bought some of the old buses for the engine, transmission and radiator and tires and wheels and scrapped the rest. Seems to me they had funny looking adapters on them, but I'm not sure if they were quite as strange looking as yours.
