These pulley kits by Balmar offer the opportunity to install a larger alternator than would otherwise be possible; this kit is for the Yanmar 3GM30. Alternator upgrades using a single drive belt are limited by the amount of power that can be transferred by the belt but using a multi grooved belt considerably increases the possibilities. The kits include a set of serpentine pulleys for the crankshaft, water pump pulley and alternator. This pulley kit comes with two belts so you have a spare, the alternators need to be purchased separately. If you order an alternator at the same time as the kit it will come with the appropriate pulley pre-installed.
Read my BLOG POST about installing one of these kits.
My blog post has installation notes for a serpentine kit on a Yanmar