If I recall correctly, the alternator on the 2QM15 is a Hitachi fork lift alternator with built-in regulator. I bought a "new", probably nicely rebuilt, one out of the trunk of a stranger's car for $140 in 2002. A month later I bought a same footprint and output Hitachi fork lift alternator without a built-in regulator for $82 (wholesale) from a large rebuilder in Glendale, CA.
Unless you are going to add battery capacity there it isn't very cost effective to add a high-output alternator. Having said that, I have two alternators on the Yanmar 2QM15: (1)a Balmar 75-90 A charging the house battery of four group 27 deep discharge batteries using a Balmar 3-stage smart regulator, and (2)the original Hitachi charging two independent group 27 deep discharge starting batteries through the built-in regulator and a battery combiner. Two of the six original batteries failed after 4 years (2-yr guarantee), the other 4 batteries are still going strong after 5 years.
