chuys84zee'

Hey guys i own an 84 na and not long ago my counter bearing decided to blow my front cover (not literally) but did crack it and i have all the new parts to replace cover, bearing and gasket. My question is what size shim should i use for the counter bearing? I called nissan and was told there's 6 different sizes! I could not measure mine as it had worn down.. Please help so i can have my baby running again :/