My truck is a 1947 one ton stakebed srw. On the one ton forum LONGBOX55 suggested that the rearend might be from a '41 1 1/2 ton. I've gone through a lot of web pages and none of the shop manuals show the large hub flange that this one has. The rearend has a large raised GMC logo and ten bolts two of which are out of order. It looks newer than the rest of the vehicle. The previous owner said it cruised at 55 mph?? It has 2000 Ore. tags and was used as a movie prop and could have have had work done previously.
here are pictures of the rearend.

https://picasaweb.google.com/Bompajohntaylor/1947HubAndBrakeDrum?authkey=Gv1sRgCJLrmv--m7ew6wE#