You turned the light bulb on , I did not consider the PTO/ Clutch Drive off the Perkins. The Perkins has a fixture there all ready to drive a geneator. I bet that Perkins has more that one configerations to drive a gen. or hydraulic pump
and other things.
I see a number of gen's.set up's for sale that (usually) mount on pick up diesels. they are faily easy to mount (anywhere). Now, the RPM shuld be at least 1000 to 1200 RPM + to get the engine out of the idle range. It's no good to idle any engine and place it under load (at idle). Bad things happen in a lug type situation i.e. low cyl. temps., water condensation, cyl. wash down due to low cyl. temp's. Four cyl. diesels have an inherit vibration problem, Some of the eng. manuf's. install counter balance vibration shafts internally to reduce vibration levels.
Amyway, great pointer to run the gen. off the aux. drive on the main engine. The former owner motor sailed this boat at -- 1600/ 1800 RPM at 4.5 knots. Thats a long way from 3,600 RPM (50 HP rating). The fasted he had the I 37 was 8.5 knt's in a 40/ 45 gale wind. His usual speed was 6.5 knots under sail with a decent wind (hull speed = 7.52 knt's.) .