That's the thing about specs - - gotta read the data tag closely!
I have seen MEP gen's for sale that put out 60Hz power instead on 400Hz power. They are out there. The one's in the pics use an Onan 2cyl air-cooled diesel.
I would also offer this advice: Stay away from anything that makes rated power at 3600 RPM's. I seldom see the "high RPM" stuff last a lot longer than 500 hrs without issues. The only exception to this rule (from personal experience) has been Honda powered stuff. Even having said that, anything that runs at 3600 is going to be thirsty and noisy.
Try your best to find something that is rated at 1800 RPM's. How big of a generator are you looking for? If you can get an old Ingersoll / Amida light cart (like the ones at construction sites) those are often 6000 watts with a three cylinder Kubota engine. I know for a FACT those things can run over 10,000 hours!!
Like this:
Amida Diesel Light Tower Generator AL4060D 3 Available - eBay (item 270729591089 end time May-02-11 08:58:07 PDT)
That seller says those are 6500-8000 hours. $2500 is way too much for that many hours, year model and condition, I see them sell every now and then for under $1000.
I have seen them with Kubota, Hatz, Yanmar and Isuzu engines. The only ones I have personal experience with are the Kubota powered ones. I don't know for sure how many gallons the tank holds, but they will run for days.