1931 was the first year Chevrolet offered a factory mounted stake body, there are no part numbers for that part. Your bed was made by an outside vendor, a local wagon/body shop or by the owner.
Break out the welder and make them or find a structural steel fabricator working on a job site and ask him to make them...bet you can get them made for $15-20 bucks or a case of beer! It looks like two pieces of angle iron welded together to make the box (box tubing has not been developed yet) with a couple bolt tabs...easy stuff!
Mike B
