Stripped spark plug threads in aluminum model 81 head

I have a stripped spark plug thread in my aluminum model 81 head. Any thoughts on best way to repair it. I have heard that helicoil threads that are steel do not work the best because of different rates of expansion due to heat. Does anyone know of a reliable shop where this could be repaired? I have contacted Lock-N-Stitch Inc of Turlock California. They said they can repair the head and have done Pierce Arrow work in the recent past. Anyone had work done there and how satisfied were you? Thanks for any ideas, Roger