[olddog]

I was hoping the porosity in the back of the intake was it.

I'm curious if the head bolt stripped when it was torqued or if it failed sometime after it was torqued. Did you torque the head down or someone else?

When you get it apart, you need to determine if the threads in the block are good. I am assuming that the block had heli-coils from the manufacturer. I would not put another heli-coil in unless the aluminum threads in the block look good. As far as I know there is only one size tap for a heli-coil for a certain size bolt thread.

Check to see how many of the head bolt threads were actually engaged. Was it a short bolt? Did the Heli-coil come all the way up to the top (recessed resulting in not enough threads)?

I agree that studs would be better. High torque on aluminum parts always give me the willies when I pull on a wrench. With studs the threads in the block never get twisted under load.