If you want to use OEM parts for the 6 lug disc brake swap, look in this thread for info on that.....
http://67-72chevytrucks.com/vboard/s...ght=disc+brake
If you want to use the '71 spindles, you cannot use the later model rotors, they're close, but not close enough. You'll have to buy the aftermarket 6 lug rotors for the '71-'87 spindles. And don't ream the spindles, just change the ball joints.
There's really nothing wrong with the D52 calipers. They are available in 2 different piston sizes also. If you're set on a 2 piston caliper, Wilwood makes direct replacement dual piston D52's. They can be seen in the 'Vendor Marketplace' in my Astro rotor with D52 caliper disc brake brackets thread here on the board.
Here's that thread....
http://www.67-72chevytrucks.com/vboa...d.php?t=398352