First... be sure we are all talking about the same thing. "Panel Trucks" have two doors in the back, "Sedan Deliveries" have a single door.
The 1/2 ton panel truck fender fits only the 1/2 ton panel truck, 1938-41. A 1938-41 1/2 ton pickup rear fender can be trimmed on the inside and new mount holes drilled. As steel panel fenders are usually easier to find and less $$$ than pickup fenders you may want to look harder. If you go fiberglass we, and most of our competitors, will sell you a pickup fender u-trim.
If you have a 3/4 or 1 ton panel the panels are rare, and the fenders are rare so pricing can be wild. There are also panels that have period coachbuilt bodies (non-Ford) and those rear fenders are often unique and who knows what fits.
If you have a sedan delivery the fender fits 1935-39 sedan delivery only, or trim down a 1935-37 station wagon fender. Again fiberglass is available.
