Brian,
Here are some links to pertinent pages in a Master Parts Catalog.
Serial Numbers Rear Fenders "SINGLE UNIT" and "SGL UNIT" refer to panel body (I think).
It looks to me that the 1 ton and 1.5 ton fenders are the same for 39-46 (and they are different from the 1/2 and 3/4 ton fenders).
Maybe someone who knows these years and how to read the MPC will post a better answer.
