It can be done fairly easily in fact. The short bed is 6 inches longer than a Blazer.
The easiest method would be to remove the skin from the inner panel. Drill the spot welds along the top inside edge and around the tail light area. Cut the tack welds in the wheel opening. Cut the skin on the Blazer about 2 inches back from the door opening as you'll have to reuse this section. Remove the skin from the short bed clamp into place and reweld the spot welds where you drilled, reweld the tack welds in the wheel opening and weld the splice behind the door opening. As long as you don't warp the splice behind the door the body work would be minimal. If your bedsides are rusted out in the lower section then you can use a section from the short bed side hammer and dolly the front edge flat and weld it in to the door pillar and weld to the splice at the front of the bedside.
The nice thing about using short bed sides is they are available new. If you don't want to spend the money on new short bed sides and you can't find any usable used sides you can always use a long bed side. They are pretty easy to find in good shape and are close enough to be used as well. The difference being you'll have to splice it in right ahead of the side marker light and the body lines won't quite match up behind the wheel opening but hammer and dolly will fix that right up.
