Kip's41: There is an angle strip welded to the bed side and it sits on top of the wood board that is next to the bedside. The angle strip is bolted to the cross sills through the wood board and that holds it all together. Take a look at our catalog page http://www.mar-k.com/earlyGMbed_kits.pdf which is a picture of the complete metal parts bed kit for a 47-53 truck, similar to yours. You can see the angle strip welded to the bedside and where the cross sills go. The wood board goes between the angle and the cross sills although the catalog picture shows the cross sills bolted up tight against the angle strip. The angle is also bolted to just the wood in the spaces between cross sills.

Angle strips are readily available and may be replaced with common tools http://www.mar-k.com/37-53anglestrips.pdf by either bolting them on or welding, although it is a bit labor intensive. Yours may likely be damaged from the plate that is welded into the bed floor.

Mar-Ktech