Adjusting rear after spring relocation?

I am about to relocate my springs into the frame. I am using a kit from RMS. I understand how to install the kit but I do have 1 question. After installation which I am going to get as square as possible which is never perfect. How do you adjust the rear to get it perfect? With the stock mounts you could loosen one side off and add shims until you got the rear square. What do you do with it after the spring relocation? I run an 8 3/4 with SS springs if that makes any difference.

Jack