The bottoming tap is to make sure you get all the crud cleaned off the bottoms of the holes. By doing so, you ensure you can run the bolt ALL the way down, thus creating the clamping pressure necessary to maintain head gasket integrity.

The main objective is to get that hole deep enough so that you're not bottoming out.

If the hole's not deep enough, you could actually torque down the bolts, but apply very little clamping pressure to the head.

87 Montero, bought new, by me -
88/89 intercooled Starion Turbo engine-
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