Avanti and/or Studebaker spark plugs?

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I aquired two sets of spark plugs, supposedly one set for a supercharged 63 or 64, the other for a 58-64. Neither number in my workshop manual. Confirm or deny?  Mike

[Dwight FitzSimons]

The J-12Y plugs are for an Avanti and are colder than the H-14Y plugs.  IIRC the H-14Y are correct for a regular 289 or 259.

--Dwight