Me and Nick (GM Duraturd) were hangin out today, and while we were eatin lunch i pretty much out of nowhere said "dude, lets put a stack on my truck" So we did.
I already had 2 5" miters layin around, just never had the bed kit or anything. But i rigged up some stuff and made a single offset stack to get me by for now. I used part of the tailpipe for a 90* elbow, then the piece of 4" i used to delete my muffler was the right length to go into the bed. Here is where the real redneck engineering comes in. I didn't have any way to adapt from the 4" to the 5", so i found an old concrete saw blade in the scrap pile, cut a 4" ish hole with the torch, slid it over the 4" then welded it. The saw blade rests on the bed so it adds a lot of stability. Then set the stack on the saw blade and welded it together. Done.
I know the pic sucks, but you get the idea. I'll get a couple more tomorrow.