Thinking about it, maybe I'm better off belt driving the generator from a pulley. That would allow me to have a belt drive 12v motor/generator for starting, or mount an automotive flex plate and starter behind the pulleys and just belt drive an automotive 12v alternator.
It would also mean I could size the pulleys so that the engine is doing 1800rpm and making 22hp, rather than around 17hp @ 1500, while still turning the generator head at 1500 rpm. Though if the engine makes enough power at 1500 rpm to run a 10kw generator head then it probably doesn't matter, and I would like to have direct drive if I could... just thinking aloud here really.