Don't need anything other than what came in the box. I didn't shim mine or use a dial indicator to set backlash, and mine works perfectly.
All I did was use a punch and mark EVERYTHING as I took the diff apart, then lined up the marks and everything went back together exactly how it came out.
The instructions that were in the kit I got were more generic and weren't really appropriate for the zook diff, as it showed an open carrier, where the zook one is closed.
I found these instructions heaps better
http://www.auszookers.com/index.php?nam ... ic&t=15661
And get yourself a workshop manual, makes everything heaps easier for the back yarder, Haynes makes a good one