OK, this brings a question to my mind now. Let's say, just for talking purposes, that we have an engine that's had the block align bored, then decks cleaned up maybe 0.020" to bring them to spec, and then the heads milled 0.040 to get the squish just right. Now, the intake has been milled to get it sitting right, relative to the head surfaces and the "China Walls" of the block. This means that the mounting surface for the distributor has dropped a bit.

What's the procedure to ensure that the distributor drive gear and the cam gear are properly engaged for maximum life expectancy? That is, how does one decide on the right shim stack beneath the distributor, or is it not that critical, considering that the distributor normally has a rough gasket there anyway?