Currently rebuilding the transfer gear assembly on my Big Bear. I'm about to order some new parts but I've struck out determining what size shims I should get for the middle gear drive. The Clymer manual states that there should have been only two layers of shims, which can be seen in my photo below. However not pictured is another half of a shim I pulled off two days ago that was hidden under some grime. My question is; how do I figure out which shims I need?