Read here....
http://www.67-72chevytrucks.com/vboa...d.php?t=452192
There is a fair amount of work involved. I've done it on a 2wd using a pickup frame and would never do it on a 2wd again.
If I were wanting a '63-'66 4x4, I would just mount the 4x4 running gear under the original frame. It is still a fair amount of work, and you will need some fabrication equipment and skills.