It's my understanding that Mercruiser made a significant change in the Generation I series in 1986 - with the Generation II Series following in 1991. My boat is a 1987 Chris Craft with the 3.0 liter engine - so it's possible that it has a "left-over" '86. There may be an "MRA" designation that reveals what it is - but the significance of the "MRA" isn't really clear to me. The engine serial number is B-645621 and the stern drive unit serial number is 0B694259. Also, the Power Package Model is 2130Y - whatever that means. I'm certain that this is all original equipment for the boat, so what do these numbers mean??? I'm anxious to get my hands on the correct Mercruiser manual.