Don't get me wrong, I'd love to have battery power on some equipment, that's how I use my bucket truck, just doesn't feel right starting the engine when I'm 40' up, especially with the rat's nest of wiring. To me, the hydraulics would be more complicated with battery power because they'd drain the batteries if you just let the pump run, you'd want something on demand, like whatever they use on forklifts, or the "emergency backup" pump that my bucket truck has.
The first step is matching the rpm. I don't know what those kubotas run at, but maybe close enough to 3,600 rpm that you can just find an electric motor around 2/3 to 3/4 the hp of the diesel. Pull the pilot pump and use the gear ratio to figure what rpm to drive it. Either with a belt or a separate motor.