Don't just measure the doors...dry fit all parts...like both the drivers and passenger's doors, cause as you can see with the back end...it looked great till you put the tail gate on.
I had a similar problem with another rig I had when I was younger

I know it can be a pain, but now I rather put stuff on, and take it off a dozen times to make sure it is correct, rather then have to deal with it after it is painted. No big deal, doing this work is half the fun
...I just looked in my files for some pics I had saved on just how much "rigging" is needed to ensure a square tub. Not just left to right, but front to back, and quite a few "X"'s tacked in for good measure...freaken thing will look like a spiderweb! Does anyone have any such photos? I think they are on my old computer