Javadoc
Sometimes a PO will change the locations of the cross sills to fit their needs, especially if you notice that the bed is not original, like in this case it has the plywood.
The cross sills will line up with some of the holes in the bed strips and the holes in the frame. Bolts go through the bed strips, between the boards, and either go through a cross sill or where there isn't a cross sill, they attach to the boards using fender washers. Bed-to-frame holes will also be drilled in your cross sills (and if you buy wood from us, would also be drilled in the wood). The bed-to-frame bolts go through the wood board, through the cross sill (or rear sill) and bolt down to the frame. Here is a general instruction (not year series specific) That might help you:
http://www.mar-k.com/bed_parts_installation.html
Another one that you might want to look at is this:
http://www.mar-k.com/bed_mounting_information.pdf
Hope this helps!