Hi Axle- On a '40 1/2-ton, the boxsides should be 79-3/4" long. They are the same from '40-'46. The front panel should be 48-1/2" wide and the tailgate a hair narrower at 48-1/4". Anything wider is later than '46, anything narrower is '39 or older. The '40 tailgate should have the embossed "Chevrolet" script stamped into it.

To be long remembered as he's cruising in
The Passing Lane