These trucks weren't available with reinforced frames from the factory. When using dump bodies or other heavy bodies, the body builder would fabricate a 1/4" plate that went from under the cab to just in front of the rear spring hangers. The plates were call "fishplates". A truck body exerts the most stress to the frame at the extreme front of the body where the body stringers end, while a hoist puts its stress at its mountings. It's usually not as hard on the truck because the truck is standing still when the hoist is used, but I've seen a lot of frames collapse and bend at the front of the hoist mounts. A properly selected hoist will take into account the truck frame strength.
Probably more than you need to know, but it explains why fishplating was done
