So it's stock running gear, six stud? Then this thread won't help much -
http://67-72chevytrucks.com/vboard/s...d.php?t=735442 ! But a TTT for you.
As an aside, I remember reading years ago that you had the Blackbird kit in your truck. I've got a Dana 60 kit in my truck with the Eldorado calipers. Been on the road about 15 months now (7000 miles). I've never had great park brake performance. Then a couple of months ago the calipers started leaking from the centre of the pistons. I now know faar too much about the inner workings of Eldorado calipers! Rebuilt both calipers and have fixed the leaks, but still have a rubbish park brake. How do your's perform?