[GRX]

"Most machine shops will look for cracks before they pressure test, and most machine shops will tell you that you have 2 big pieces of scrap metal."

Agree. They are junk. What you describe is the proper way. However, when Magnafluxing, the heads must be thoroughly cleaned first so the solvent carrying the flouresing agent can be drawn into the cracks when the magnetic field is applied. Some shops will charge extra for cleaning, others not.

"Machine shops can only pressure test the combustion chamber. They cant pressure test the coolant passages."

We can pressure test the coolant passages just as easily. It's essentially the same thing.

Above said ... the crack from coolant passage to head bolt hole could be welded. The ones at the seats are bigger problem since far larger temperature differential there. Much cheaper to buy different heads that try to repair.