Thanks.

Any idea how much the head bolts actually stretch when tightened?

I managed to get it tapped what looks to be deep enough - .18" beyond what will be required to have the bolt tight against the head with a head gasket in between. I should have at least .15" for bolt stretch and I can't imagine even those spindly little bolts stretching .1" with ~ 48 ft/lbs of torque on them.

I could probably tap it a little further down but I'm afraid that every time I run and tighten the tap that I am removing a small part of the threads, even if it is a small amount.