Be careful. Yanmar
3GM30F are real good engines, among the best. But nothing's perfect. 3GM30's front end bearings are a little weak, and alternators soak up a lot of power, so that installing a bigger one may overstress the front end.
In Charleston SC USA I had two Yanmar
mechanics in to service
my 3GM30F at different times. Both asked, before they came out, if there was any modification to the front end, that is, a bigger alternator
. If I had said yes, neither would have touched the engine
Touch base with a Yanmar shop or distributor.