I'm very impressed with the XRay vision of your tech. How can he possibly know about the head without removing it and inspecting?

There are several things that could be wrong with the head, but all of them can be repaired by a competent machine shop. Most likely it is not straight or it has corrosion between water jacket and combustion chamber. A good machinist can weld up the latter and straighten the former.

The same concept carries over to the a/c problem. Don't diagnose until you have investigated. If there is a little charge in the a/c, charge it up with UV dye and then look for the leak. There are many sources of problems and leaks besides the evaporator. You can't just assume that the evaporator is the problem without diagnosis.

Would you go to a doctor that prescribes medicine without first examining you? I hope not. In the case of engine problems such as this there is no way to know until you take it apart.

If your engine was running good and not using oil before this happened, I personally would prefer doing headwork on that engine than to roll the dice with a used engine of unknown condition.

My $0.02,