Mike - Here's the link to an original
1940 Chevrolet Truck US sales brochure. Nothing in there resembles your wood hinged drop sides of this Australian 1940 flat bed. Nearest thing in the US pamphlet is the stake side platforms which in these pics where all the lift out removal style side panels. Another unique feature of the trucks from "Down Under".
Your pictured drop side panels sure do remind me of some of the earlier Army cargo trucks I used to wrench on back in the day though. Some of those had metal hinged fold down side panels with wood side cargo panels that fit into side panel stake pockets for added height and cargo carrying.
