All in all a very interesting truck. I think we agree the delivery date is a miss strike, as stated by Keith ten years ago.
Edbro has been around since 1916 and they still thrive:
https://www.edbro.com/en/profile.html
They did deliver tippers during WW2, but mostly on British trucks IIRC. Reading that they always exported conversion kits, I think this is most likely a postwar conversion.