I have seen a lot of kits advertised. Back of fourwheeler magazines and such. Do a google search on disk brake conversion and you'll find a bunch. I even think that Summit has one in there magazine.
There is a right up on fullsizechevy.com, check that out.
As far as quality. It's just a bracket and caliper, seems pretty simple. Make sure you get a caliper with a parking brake. I'd be interested in what you find out, a friend of mine was just asking me about this also for the chevy axles under his jeep.
-Chris