I am working on a '46 2-Ton dump truck. Something didn't look right, this truck was very much rebuilt/modified.
A think someone removed the reinforcement plates from both sides of the frame, also the runningboards and brackets. They removed the rear springs and axle, which left the outside of the original frame clean and bare.
It seems they had a donor truck, that was cut off under the cab floor, it may have been complete with the dump bed. This rear frame assembly was cleaned out by removing all crossmembers and hardware,from the inside, leaving the rear axle assembly and springs installed.
Then the donor frame was slipped over the original '46 frame, telescoped, to the correct wheelbase, the outside plates were re-installed, and now is a 3-thickness frame!
Note, the donor frame top flange was cut off behind the '46 cab, the bottom flange and side end just behind the front spring, matching the frame outside plate. A very professional looking job!