According to some research on Chevrolet archives, the bed location holes were not drilled at the factory until the bed was aligned on the chassis, then the mounting holes were drilled from below thru the mounts...
There are so many variables involved, how and where the wood planks originated from and the drying treatment etc, the mounts themselves on the chassis etc
I would really value your measurements from your install process tomorrow, as I will be undertaking this on my own long bed this fall.
As always, pics are best...plus detailed measurements..edn of board to center of each hole, distance in from rebate edge, etc
Have a great day...
