When I repaired generators many years ago, the small gennys on reefer trucks were 3 phase 240 delta. I don't know if they where available in anything larger than 5 or 10 KW.
If the Guardian you are talking about has a 12 lead alternator, you could rewire it for 120/240 delta with a high leg. I would check with the factory about the maximum unbalanced load.
