Mike,
I checked my (original) 1940 1/2 ton bed as well as my rebuilt 1937 1/2 ton bed and they are the same. The first metal cross support is only a couple inches from the front of the bed. A 2 1/4" wooden block and a 1/4" rubber bumper/shim sits on the frame at that location. A long bed bolt goes down through the side bed strip, through the metal cross piece, the block and the rubber shim, then the top rail of the frame and bolts there.
The next metal cross piece is approximately 24" o/c back from the first cross piece. This one does NOT have a wooden block, but is fastened through the bed strip onto the underside of the bed. This cross piece does NOT ride on the frame rails, but floats just above them.
The final metal cross support is approximately 26" o/c past the middle support and near the end of the bed. An approx. 3 3/4" wooden block and a 1/4" rubber bumper/shim sits on the frame below it (like the first support); the holes in the frame should make that apparent and should line up with a bolt hole through the bed strip that will accommodate a long carriage bolt that will go through the bed strip the cross support the block and shim and the top rail of the frame and bolted there.
The rubber bumpers/shims are like those in most body mount kits--they probably were included along with your wooden blocks. The original blocks (and replacements) seem to be of a wood akin to poplar; they could be made easily enough if you don't have them. When everything is lined up correctly with the bed and the bed strips, this scheme should become readily apparent. I have replaced beds at least twice on various trucks, and it's a lot easier to construct the bed off the frame if possible--rather than lying on your back and fishing all the bed bolts through, etc.
Your metal cross supports should be drilled (factory) to line up correctly and accept all the bed bolts and frame bolts in their appropriate locations.
I hope this helps! Good luck!
Jim
