Wood bed intallation problem on 72 LWB

[Orence1]

I am in the process of installing a wood bed in my 1972 LWB. Using the diagrams and instructions on GMC Paul's web site I created the boards from scratch using oak. The length and width of each board conforms to his diagrams. My problem is that when starting out from the other edges and working my way towards the center I am left with a gap in the middle that is too wide. The strips and the holes in the tailgate end line up with the exception of the middle. I would make sense just to slide each board a bit towards the center to compensate but then the tailgate end holes will be out of alignment. I was hoping that some of you that have successfully installed a wood bed might have some suggestions as to how to solve the problem. Any help appreciated.