Here is a list of s/ns from 1979 thru 1996 so you can see the format for the s/n. This is a s/n from 1990, 689-036668 but when you see it on your engine, it will look like this 689 L 036668 or the letter may also be S, U or X.
http://www.marinshopen.se/Motorer/O...årslista/Mariner2530hp/tabid/460/Default.aspx
Gerry
I don't think those numbers you posted are anything to do with the s/n. see if you can find a disc like this on the power head.
http://img84.imageshack.us/img84/8224/391496208.jpg
Gerry