It ca be quite simple to do. It also depends on how much of the susp[ension you want to change. You will also have to upgrade the master cylinder, which is also a good time to add a brake booster. Then of course there is the power steering upgrade to go along with it. Most all of the components can be found on the same donor truck. Here is one thread that explains most all you need to know about upgrading to front disc brakes.
http://67-72chevytrucks.com/vboard/s...d.php?t=367260
I believe there are a couple more in the '60-'66 FAQ Index at the top of the page.