crew cab short box conversion

[c65shoebox]

how much do you need to cut out of the frame to do a short box conversion?  Probably lining up the cab on the frame, then lining up the short box on the frame at the rear or the frame and then just getting the dimensions necessary to cut?

[Captkaos]

http://www.73-87chevytrucks.com/lwb_to_swb.htm

14" behind the bed, and 6" off the rear of the frame.