The E3.72 spark plug that’s called for a Y in the E3 listings happens to be the same spark plug as also listed for the 352 FE. In looking through the crossover list I could not determine which Autolite or Motorcraft spark plug crosses over to the E3.72 plug though.
But I would like to run a set on the dyno mule just to see where the heat range falls as compared to the other spark plugs that are being used. While I’ve found that the spark plug gap is a non-player in regards to horsepower production up to point that the gap is increased so much that misfires occur, the heat range on the other hand is a significant player.