Given you can cut out frame pieces accurately to shorten it, re-join them securely, and have a location for the fuel tank, etc, I see no problem with your idea. It is best not to weld the top and bottom flanges of a truck frame rail just in case they are tempered, so a long, tight fitting splice, inside and outside the rails, held in place with high grade bolts is best. It is really good if you can find a frame rail piece off another truck that fits nicely over the outside or inside the Deuce frame rail for the splice. Failing that, cut the flange off one side of the cut out deuce rail pieces, place one over the outside with the flange up or down, the other inside the rails with the flange in the opposite direction. Solidly bolt through.
Regards Marti