The plugs are normally steel. I have an ancient wrench for those plugs left from my 62 fintail. It has a hex on each end with one end in a kink for access. There is no offset so you can put it in and hit it with a big hammer. It always works. Make sure the hex is well seated and you don't allow the hex to slip sideways and ruin your plug.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.