are you saying he's going to port the head with the head still installed??? that sounds like a recipie for disaster in it's self.. regardless if he screws up a porting job or not (which is possible).

He told you that by stuffing a rag into the head that he will keep any chips from getting into the cylinder? <interesting> How about see if he will guarantee his work and replace/fix the engine, just in case something gets past the rag (which could wreck the cylinder wall, valve seat or seal, etc)