For what it's worth, the 47-54 Factory Assembly Manual (Section 11, sheet 2.11) shows a shim on top the frame, as well as additional (as-required) shims, and a body shim (square) under the frame followed by a fender washer, lock washer and nut torqued to 18-20 ft-lb. No springs. I'm guessing the earlier trucks were similar.
