[David_Hayward (RIP)]

Right, this is clearly a GMC truck, and I am taking a stab as being outside the GM Continental SA factory in the Bassins in Antwerpen/Anvers/Antwerp. If it is the same as the US version it is a GMC Model 4929, which was available in 1938 and 1939 apparently and then for 1940 it became the ACKW-353. The 4 x 4 equivalent was the Model 4930 based in 1938 on the T.16B, and then available again in 1939 and then in 1940 became the ACK-353. It appears to be a chassis with flat-face cowl, so the cab would have been built by GM Continental. If it is one of these then I suggest that the rear bogie used a Timken-Detroit rear transfer case. However it could also be a Thornton conversion as these were offered by GM. Can any sharp-eyed viewers confirm either way?