I would guess that is the GMC equivalent of the Chevrolet Model 3103 (cab/chassis w/rear fenders but no bed). There is and example of this version in the 47,48,49,51,and 54 Chevrolet Salesman Data Books so it must have been pretty common for people/companies to construct their own beds. Go for it another truck on the road and being enjoyed is always a good thing, good luck!
