V 12 original spark plugs

[atomman]

What were the original spark plugs used in the GMC 702? I am currently using Autolite 403 plugs. Are there Champion or Delco plugs? Is there a better recommended plug?
atomman
Dan Marx

[LEWISMATKIN]

that depends on the heads you have on the 702. early production engines used an AC C42s, later engines used the C-44NS. this also covers replacement heads because all replacement heads until 1972 used the "N" series AC plug.