A friend has a shiny new Kubota 4400 tractor, and we were planning to get a 3-ph PTO generator for it.
But reading further, the Kubota PTO itself is just a hydraulic motor. [So are the drive wheels, for that matter.]
So I am thinking a better scheme is generic generator, driven by a hydraulic motor with quick connects. That way, you just pull up and pop in the lines. Besides not having a driveshaft in the open; the plus is we could drive it off other hydraulic sources he has. These include a Fiat-Allis bulldozer, and similar toys.