I think it is the third large cross member from the front that is different from the rest on the longbed. I know that putting in the wood can be a lengthy and tedious process. The hard part for me was keeping the bed square while I tightened the boards up. I didn't have any help, so I placed mine upright so the tailgate was up near the ceiling. Then I used a tiedown strap to pull the side over one direction till square. I put all the boards and metal strips in with all the bolts (loose) Then I used some winch straps to pull the sides of the box together to make it as tight fitting as possible before tightening it up. It's not perfect, but the next one will be better easier.
