if you can get some pics of your new roof I could give better advice.
I have kind have done the same thing when I sectioned my 60: here is a link,
http://67-72chevytrucks.com/vboard/s...d.php?t=280904
as of now I would say leave your doors on and lined up, this will give you a line to follow when putting the cab back together.
maybe cut the door pillar above the door latch, so you don't have issues getting the door latch to line back up.
make sure you have all your measurements done before you cut. I went around my cab and put the lines to measure from, and then just wrote the measurement right there so there would be no confusion.
on the front roof pillar the inner "dogleg" is spot welded on, if you can don't cut it, drill the spots, and leave it as a guide to line up the new roof I did this (n that link I gave you on post #2) on my suburban, and it worked out nice.