Hey Sean,
By no means I'm I an expert on this subject but personally I would never ever crack a case open to check shim clearences if its working good.
I've rebuilt a few OD and re sealed a few more and I only check end play and shim clearences when replaceing bearings and other internal metal parts.
When I re seal an OD I put all shims in exactly the same place they came from and theirs never been a problem.
If you want more info get on the Hull Truth web site