Please post your Predator model. I recall that some had the 30A/120V receptacle.
Will look at HF and see what I can find.
When you use a four-to-three A-Dapter, you're passing ONE of the two 240-volt legs through, NOT combining them. Combining would be a dead short.
Inverter gennys, and HF has a few, like Honda 2000/2200, can put all their wattage to one circuit. So can RV generators.
Looking more and more like open-frame jobsite genny providing 2000 Surge and 1600 Run per 120 volt leg. You can do that twice, like A/C on one leg and microwave on the other. But they have to be on the opposite legs.