There are a couple ways to get 6 lug disc brakes. One of the simplest would be to just purchase '73-'87 droped spindles and the springs of youe choice along with the aftermarket 6 lug rotors. Then you just change your balljoints to the '73-'87 balljoints. If you can find the parts, I would suggest changing the entire steering linkage to the '73-'87 components. This will attach to the spindles without any special adapters. However to install that newer steering linkage, you will have to drill holes for the newer idler arm. Are you converting to power steering as well? The main drawback to this is that you are locked in to using the aftermarket rotors. You can't just go down to an auto parts store and get a new one if need be.
There is another way, but there have been a couple guys report camber issues. I have not heard back on whether or not they have gotten the issue resolved. Anyway, here is a description of what is needed in this thread in post #16.
http://www.67-72chevytrucks.com/vboa...d.php?t=367260
This version uses all OEM parts that can be sourced at most auto parts stores.