8 3/4 pinion shim question

Here is a pretty clear explanation of what you are trying to achieve. Not Mopar but the idea is the same.

http://www.streetrodstuff.com/Articles/Drivetrain/Rear_End/Page_2.php

Here is the tool you need to get to do this correctly:

http://www.summitracing.com/parts/SUM-900021/

There are 'better' (more expensive ones) that install where the adjusters are when the caps are on like this one:

http://www.markwilliams.com/detail.aspx?ID=1405

I have the cheap one but never used it because it's a universal deal and is clumsy. I took the plunge and got the MW one. It's a beautiful piece and makes the job easier.