Fleetside bed question

[Leadfoot Lambert]

I started working on the bed of my truck this weekend, I have to change the drivers bedside because its junk, I also have some body work to do on the pass side but I figured I should probably make sure the bed is on strait and square before I start. Here's where the fun starts, it seems the bed is narrower than the cab by over an inch! There is a slight bow to the head board but its not bad enough to pull the bed side in an inch, so what gives? Is the bed supposed to be narrower than the cab? the cab is on strait and has all new mounts, the nose is on with new radiator support mounts and a rust free California radiator support, everything in front lines up very well. the bed could be on crooked at the front and maybe I should move it over to split the difference but the drivers side lines up near prefect now. Here's some pics any suggestions appreciated