HELP! Mercury outboard ID help.

[Kongfish]

Hi,
I just bought a 1997 trihull boat with a mercury outboard on it. It's a v6 but I can't find anyone who can tell me exactly what motor I have so I can order parts for it. The plate on the transom is blank where the serial number is supposed to be. I have the engine block bolt serial number but I can't get anything to pull up under that number, can someone out there tell me how I can go about positively IDing this motor? My engine block bolt serial number is # C289990 I can even download a picture of it if you want to see it for yourself. Is there a part I can use that part number to trace the part back to say with that part number the motor is a xxxx unique to that size mercury motor? It is a V6 carbureted mercury

[boats.net]

Look for a round aluminum plug on engine block with serial number stamped in it but still would need to know what horsepower it is to id it. Without some numbers there is no way of telling for sure what model it is.

[Kongfish]

That number is C289990 I think it is a 150 its a carb.
Is there a certian part I can get a number off of that will tell me exactly what I have? Here is a photo of that plug

[boats.net]

If a 150 then would be a 1990 model year.