Browsing through my Original Parts Group catalog they have a complete kit for $765. Supposed to include everything you need for the conversion. You might find some different set ups browsing around. Try different El Camino- Chevelle shops, I'm sure they all have conversion packages.
Just found an article in Super Chevy. Go to www.praisedynobrake.com They have a complete drum replacement kit for $745 that does all 4 wheels. According to the article they were very impressed with the results. Something to consider.