I was thinking my dump bed was from a later model truck. Looking at the photo of this '40, mine looks a lot like it. On mine, though has a oval opening in the support web of the bed, and a spring clip on the rear one for holding a shovel on either side. On the pivot connecting the bed to the frame, it says 'Wood' on the casting. Also, the PTO knob says 'Chelsea', but I'm almost sure that's not correct.
Tom
'38 TB