I have Edelbrock #60899 Performer RPM cylinder heads on the 327 in my 57. Edelbrock calls for Champion RC-12YC as a good spark plug (for street applications). Any alternative recommendations? I pulled the plugs in order to hand rotate the engine more easily, and I find that two of the ceramic insulators slide up and down the electrode . I don't know how that happened, but might be a good opportunity to switch, should there be a better alternative.
Thanks, Doug