This would be a really long shot.. but have you considered asking GM if they have any records on the truck? Perhaps if you are able to sell them on the historical significance they might lend an ear and look though their records. I would think they could at least tell if it was US or British if the records still exist. Or maybe find groups of serial numbers and see if yours falls in. I'd imagine most military orders came in lots and the lot might be easier to track than the specific truck. It'd be really cool to find out, but it's far from an area of expertise for me, just brain storming. Good luck!
