mart correct, we forget how much a frame flexes under load. They all do. Why a radiator and motor is not bolted tight to frame either. Radiator springs go under the frame, not the top like a shock. 38 trucks had spring under all 3 gas tank bolts.
I was lucky enough to have a nonmessed up truck, so I reused the steel wedges and whatever I could save. Bed on a 38 has no springs under it. Just the cab.
There is webbing on top/bottom of the wood.
You could substitute the original springs with valve springs but not the same totally (bit smaller diameter spring). Springs create a system of flex, Reason for castle nuts and cotter pins.
What I couldn't save, I acquired here
http://fordscript.com/