All that matters is getting the gaps as close to perfect as possible so whatever you have to do to accomplish that within reason is the right thing to do.
A lot of times guys will add metal to the door to close the gaps instead of messing with the cab structure, so get the cab as close as you can and do the rest of the adjustment with the doors.
Here's an example during the mod and after.
http://67-72chevytrucks.com/vboard/s...&postcount=674
http://67-72chevytrucks.com/vboard/s...&postcount=675