If you need the frame channel, as in cut from another truck so it can be welded to your truck, this might not apply. The Master parts catalog says that a complete frame or frame side rail is 1939 only. If you need the forging that goes in the channel to provide a spring hanger and bumper mount, the catalog says 1937-1940 all 1/2, 3/4, and 1 ton trucks, EXCEPT 1940 1 ton. I hope this helps.
Back to the frame channel. It is likely that the front portion of the frame would be the same for at least 1940 but I have no way to confirm this.
Mike
