I have a 2007 Marine Power 340HP in a Tige 21i. The spark plugs currently in it are AC Delco 41-993 (PTR4G-15) These codes are easily found on the net. To perform a cross reference in Australia, there is no such beast according to NGK. Apparently performing a comparison they came up with a ITR4A15. Has anyone heard of these before and are they OK???????