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what about champion C-63YC

would it be a better choice?

Definetly NOT There way to cold for a low compression pump gas motor unless you run it really lean at idle and part throttle, I wouldn't. Champion uses a numbering system that the smaller the numbers the colder the plug is The C63YC is a 5/8 body plug with a protruded gap and a copper center electrode that is a little hotter than a RN6YC or N6YC would be

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)