There are many of the generators in use today that you are referring to . The generator it self is mounted on a 3pt skid that will attach to the back of a farm tractor. These are used in many dairy operations to keep the milking operations and cooling going during a power outage.
50KW and above are the choice for a small milking parlor. The prime power for the generator is usually the old ford or massey tractor that was wore out 20 years ago. No electronics and no computers. Just an old farm tractor with a basic generator running off the PTO.
The gas models use points for the ignition. The diesels use glow plugs. Very basic and sturdy.

Try giving this place a call:

They probably know more about it than either of us.