Also- here is a site that shows depictions of good and various bad contact patterns.
http://www.precisiongear.com/pgtechpatterns.htm
I just got done building a rear for my Camaro, so this stuff is still fresh for me.
After doing the work of properly setting up the rear end, I began to understand why some people can justify spending $2.5 to $3k for a bolt in unit.
Best-
S-D