It has one handle. and one pedal on the left
Rear pto doesn't define it - both had the option of a rear pto.
As you sit on the machine are there 2 handles on the left side engine cover next to the steering wheel or just one? 2 would be the Kohler, 1 would be the onan.
Or open the hood. Kohler will have 1 spark plug lead on top of the engine. The onan will have 2 spark plugs (and spark plug leads), one on each cylinder bank sticking off to the side.