In pursuing the Balmar site, looking at the power output curves, to achieve the desired 80 ampere your looking for it appears to be necessary to jump up the the 100 ampere range of alternator; using a 2 to 1 ratio pulley to run the engine at 1,200 RPM to achieve the alternator 2,400 RPM and 80 ampere output. You will not achieve the full output capacity of the alternator but you will get the desired output you are looking for.However, with the maximum rated horsepower of the Sabb G-10 is 10 HP and the continuous rating is 8 HP, considering 1 HP/25 ampere of charge, leaves you with 5 HP to make way. This configuration is fine for charging at anchor, but if you attempt to leave anchorage under power with low batteries, the alternator will kick in, leaving you some what under-powered underway.
You could install a simple on/off switch in the field circuit, this would stop your alternator from charging and get back the 3 HP if needed in an emergency.
Marty Chin, BCC Shamrock