L/C Advanced handling sells them, I think that they are the only ones that sold a "bolt on" deal, which is something that I would not want anything to do with. Was in Moab in '95, saw two 40's running these set ups, both trucks broke bolts on the trail. Welding this set up is the only way to go.
I run, as do many people I know, the MAF kit, works for me, and others.
I think that Classic Cruisers sells something that uses the orignal rear spring hangers, which are parts that you already have on your truck. Do a search for shackle reversal and read on..you should find pleanty of info...
-Steve