Longstep to Shortstep conversion??

[72bigblock4wd]

I have a 67 GMC C15 longstep that I want to turn into a shortstep. I've got a friend with a steel fabrication shop that can handle shortening the frame, and another friend who is doing a frame off on a 72 shortfleet with the same drivetrain as mine who has an extra driveshaft. What I'm unsure about is cutting down the bedsides from long to short wheelbase. I'm thinking I should be able to dissassemble the bed and cut them down to length. Has anyone out there done this with a stepside bed or can someone with a shortstep tell me the measurements of the shortstep bedsides?? What I really need for measurements are how much to trim out from in front of and behind the fenders. I'm assuming it's the same 12" in front, 8" in rear, but I want to be sure before I start marking things to get cut down. Thanks!!