Way back when (mid-70's) I started out racing VW Beetles. These had aluminum heads and stripped spark plugs were fairly common. There were a few different kind of inserts available for repairs (heli-coil and a couple of rigid ones). However, any of these cut down on heat transfer from the plug to the head, and on a hotrodded motor you were much more likely to get detonation and burn a piston or valve, or just burn up the spark plug tip. I'd call someone like Gene Berg Enterprises or Claude's Buggies and see what their opinion is. You may have to actually weld up the hole and redrill and tap for a reliable fix.