Truck bed mounting is important and people have worked out the details years ago.
I've seen instructions in old manuals but can't seem to find an online reference readily.
The gist of it is don't weld, don't drill into the top flange of the frame, or drill the side rail any closer to the corner than the flanges are wide.
Generally beds are bolted down with U-bolts around the bed long rails and truck frame rails. Legs of the U-bolts pointing down and a thick flat bar with two holes to match under the frame. If the frame or bed long rials seem flimsy at the flanges the space between if filled with a small wood block (end grain up) to support the bed and or truck frame just where the U-bolts are, usually notched so the inside U-bolt leg keeps it from falling out.
If the frame is long or the bed is exceptionally stiff heavy springs are used between the u-bolt plates and the nuts on the rear most several sets of U-bolts. This allows them to move somewhat independently and not break one or the other.
The front (or sometimes the rear) of the bed is often more securely bolted to the truck frame so it won't slide forward or back. One method is a 4-5" piece of angle iron bolted to outside of truck frame, second flange pointed up and matching angle bolted or welded to the bed frame, the two remaining flanges are bolted together.
Bed is usually isolated from the frame with a 3/4" or 1" or up to about 6" piece of wood. Modern trucks still use wood or there is a 1/4-3/8" plastic strip sold for same purpose. This may need holes drilled to clear rivet heads.
Mounting the bed on rubber mounts sounds risky, and or the reward is negligible. It's an old heavy truck, it'll ride like one.
Anyone have old factory literature on bed mounting?
