Helicoils are widely used for spark plug holes and, from my own experience and research, appear to work just fine. Starting a fire over this and sending everone to the closest machine shop to have their heads redone with bronze inserts does not feel like the best advice, and may not be your actual intent, but people could think it is.
Additionally, Whitworth and BSF wire coils made by Recoil (an Alcoa company) are readily available from various sources.