I am replacing the spark plugs on my engine, and the manual calls for Denso IK24C11 plugs. However, it does not appear that Denso makes these any longer. I cannot find them on their website (although IK24 plugs are available). I have been given various conflicting answers about plugs that cross-reference (including Denso 5311 and 4709). How do I go about (1) finding the specs from the old plug and (2) cross-referencing those to a new plug.