Jim, first off I'm a Dodge truck/Cummins guy. Rebuilt a couple of 5.9's and owned 3. Still have my 95 3500 with a turned up Cummins that's at 250k miles. No problems ever.
The above said, I became enamored with the Isuzu diesels a few years ago. They are easily sourced, easily adapted to automatic transmissions, turn more rpm than the Cummins and most importantly, much quieter. Also since the donor vehicle is a commercial truck they would certainly be up to powering a Big Bolt.
http://www.4btswaps.com/forum/showthread.php?7348-Isuzu-4BD1T-Introduction. This is one link to a conversion using a 4BDIT, 3.9 engine. The bible for Isuzu conversions was located here;http://www.isuzudieselswapper.com/
However now the site is down. The developer, Dave in Florida was selling conversion kits and actually sold a new pickup on ebay that he'd converted to the Isuzu 3.9 diesel. Someone with internet skills could likely use the Way Back Machine site and pull up Dave's old information. Unfortunately that's not me.
My dream conversion has long been a late 80's early 90's Jeep Grand Wagoneer with the 3.9 Isuzu. Plenty of power and 30ish mpg.
