I was experiencing fading batteries that were having difficulty starting my 2GM20. I thought that the Alt may have suffered an untimely demise.
I took the old 35 amp into the local Advance Auto parts and they tested it, yup, it was dead. They told me that it was the same frame as the NISSAN alternators and that they could have a 65 Amp on in 2 days for about $75. I did a Ebay search and found a 50Amp Hatachi for a Yanmar for under $100. I stayed with the marine version for the few extra $$...
Cal 9.2 #19 SilverSwan