everything is relative to everything else, if the cab mounts aren't correctly positioned, it's not likely the cab will fit on the frame - and the reverse as well .... if the truck is basically functional now, you have the measurements .... if you need to know how to fit the doors, see the shop manual 'Body' section, where you'll find final 'suggested' positioning relative to the openings
you'll find every one of these trucks is an individual, it's common to have to fiddle to make parts from one truck fit on another, and aftermarket patch panels are generalities that have to be massaged to suit your individual - document the condition now and be ready for some frustration
Bill
