On p. 246 of Les Freaty's British Military Trucks of WW2 I found this interesting picture of a Ford CMP F15 4x2 truck fitted with a British-built cargo body.
My hypothesis is that these trucks were originally assembled as Truck, 15-cwt, 4x2, AA, Mk II, more often referred to as a 15-cwt Polsten AA truck (or similar).
When due to Allied air superiority this type of AA truck was not needed anymore, they were re-bodied with GS type bodies commonly found on British 15-cwt trucks.
