If you want to keep the bed at stock height move the angle strips up on the sides, put an angle strip across the front panel and a spacer between the rear bed crossmember and the new bed floor height or leave the gap and put a panel between frame rails to hold a spare and tools---kind of a poor mans Cameo. Longer bed mount blocks will fit between the frame and raised bed crossmembers. This 51 GMC sets on a 72 Cadillac Sedan Deville frame which has huge kick ups for the rear coil springs. With the repositioned angle strips the bed is only eight inches deep (about directly behind the GMC letters on the tailgate) but it never hauls anything anyway. Some just mount the bed and leave the floor out. Still think this job only takes careful measuring and common tools. If you want it to be a high point restoration then disregard above.

http://s32.photobucket.com/user/coilover/media/51GMC009-1.jpg.html

Evan