Thank you, Cadin. That's a seriously neat swap you've got!

I haven't checked the vacuum shutoff with a vacuum gauge, that's the next step.

The Delco 22SI is 150A continuous duty. I measured voltage at idle with the stock 300SD alt and only the fuel lift pump running, 13.2V. Waited on the cooling fan to kick on, 13V. Started adding wipers and HVAC blower and headlights and voltage quickly sagged to 12.7V - battery voltage. Rev the motor and voltage rose to 13V. It just ain't keeping up.