Shim for Used 8 3/4 Gears

I purchased a slightly used ring and pinion from a friend. Only had handful of passes on them. However after reviewing Mancini's guide for installation I am unsure how to determine what size shim should go under the pinion bearing. He removed the bearing and shim and threw them away. Also no paint was marked on the ring gear. According to the guide without that if I don't get the wear pattern correct premature failure will occur. Maybe they are a little too critical in the guide.

Anyhow can I use the ring and pinon and how do I determine which thickness shim should be placed behind the pinion bearing? thanks!!