There's no reason you can't convert it to a 5 lug wheel bolt pattern. Everything changes out the same as on a C10. The exception to that is the lower control arm shaft is an oddball. It would be easiest to just switch the complete suspension crossmember with a '73-'87 unit. There is a way to go with 5 or 6 lug discs on the front by using '88-'98 components. Check out the 'Disc Brake Upgrade Reference Thread' That info is on the first page.
http://67-72chevytrucks.com/vboard/s...d.php?t=367260
Ther are a lot of links to good info in the '60-66 FAQ' section up at the top of the page
There are a couple of options for the rear end. That depends on your cutting and welding skills.