[dsraven]

on my 57, when I got it, the doors sagged really badly so the doors needed to be lifted to close them and get the latch to catch and I just thought the hinges were so badly worn that was the problem. turns out the truck was in a crash at some point so nothing fit. the "average fit" method wasn't gonna work. I opted to use the 58 cab I had because it would be less work to fix. since you don't have that option i would close the door and wedge it up here and there as required to make it fit the opening as best you can. little wooden wedges work great for this or even a slice of thin plywood sitting on the step under the door. short lengths of wooden paint sticks held in place with duct tape can also be used to set gaps so it is easier to get the door centered when working alone. the doors were made to fit the cab they were on when at the factory, as well as the hinges, so a door from one cab, that foits that cab well, may not fit another cab so good. anyway, my point is, see if the door will fit the cab opening without worrying about hinges. hinge pillars etc.if you get it as centered as possible you should be able to see if the cab has been tweaked. like posted earlier, make sure the glass fits. before you go ahead with cutting and welding anything on the cab it's best to fit the doors in their openings and then cross brace the cab across the openings so when the doors are removed and hinge pillars or whatever is cut and new parts are welded in you can be sure the opening doesn't get pulled out of shape. it's good st start with the cab bolted down to the frame on a new set of rubber mounts at the rear and shimmed at the front as needed so the cab is level with the frame. the factory assembly manual will have dimensional specs on stuff like that gap between the frame and cab. get that done, then check the glass fitment, fit the door, brace the openings, brace from side to side behind the dash so the cab can't be tweaked then the cab can be taken off the frame if needed without worry that it could be slightly outta shape by the time work is done and it gets put back on the frame.
just my 2 cents after having cut a lot of metal out of my cab. floor, firewall, rear wall, pillars, etc. not much left to hold things together but with the bracing it all fits again, as well as could be expected