Here's a link that might save you some time at the junkyard.
I got most of my information from the same thread that Rattlewagon linked above, here some pics:
New front spring hanger placed 11" forward of the factory one (hole to hole). Be sure to line it up with the old one to get the springs straight.
Some guys get away without moving the shackle mount, I didn't. You've just got to tack and cut until you get the right shackle angle, mine was 3-4" forward.
I would suggest buying all new spring hangers and shackle mounts, they're just too thin to cut off and re-weld IMO. I went with creeper joints and don't have any real complaints.
They ride pretty smooth, flex well, and have way better departure angle than Chevy 63's.