Here are a couple of links with info on this swap. Swapping the entire crossmember over is very straightforward. There are only two bolt holes that need to be modified. Also, parts for the newer style suspensions are very cheap.
http://67-72chevytrucks.com/vboard/s...ht=crossmember
http://67-72chevytrucks.com/vboard/s...d.php?t=208939