Kits can be purchased, but I think the best approach is to find a donor 71+ C20 setup. 73-87 may even be preferred to 71-72. At the very least, less expensive, more common/available. Makes finding/buying replacement parts much simpler and provides factory power disk performance. Price depends on how good a deal you get at the junkyard on the parts. Can do a crossmember swap or every thing but the crossmember, I believe, but some considerations regarding lower control arms. I haven't done this swap, so can't really tell you if it's painful - but if I WERE going to so this swap, that would be how I'd plan to do it.
A couple of threads for additional info:
http://67-72chevytrucks.com/vboard/s...d.php?t=763609
http://67-72chevytrucks.com/vboard/s...d.php?t=536728