do ac 41-983 come pre-gaped @ .060 ?

OK, just got off the phone with NGK. They actually build the AC Delco plug recommended for the 490 HO. They suggested to use the 993. Because of the close proximity of the ECU. And both of those plugs are platinum. If I did switch to NGK they suggest a PTR – 4G – 15, long-lasting. Or on the performance end and must be changed more often a TR-55ix

NGK must not know about what Mercruiser overly based 2 stroke motor oil mix for winterization at 10 to 1 does to the plugs especially on the 496. You basically have to change the spark plugs out every year or every other year because of Merc OEM winterization procedures. ( the winterization soup mix) Anyways that's another reason I do not go under 50 to 1 ratio mix.

also if you were to buy the recommended spark plug thru a Merc dealer under the OEM part number listed - it comes back as the 983. I still would use the TR55Ix and that is correct NGK does make some of the AC Delco spark plugs especially the ones used in apps for Merc. Mercruiser and Volvo and so on. .

IMO the NGK TR55Ix seems to produce a TAD smoother idle and seems better suited just off idle acceleration and IMO again in apples to apples comparisons. I sure have worked on enough of them and had to change many spark plugs out in 496's. The early 496's with Denso spark plugs were junk almost right from the start. Also a special note I have some cases where NGK's had a bad plug or 2 right out of the box thru out the year but not on this plug.

forgot to ad - I understand the NGK recommendation as well - they want a better EMI and RFI suppression spark plug installed because of the close proximity Marine ECM / PCM locations and harnesses.