Note the following:
"It was originally installed by a municipality there to provide emergency back-up power. There is no generator with it now"
If that was really the case then I would reasonably expect it to have the heavy flywheels fitted, instead of lighter spoked versions. Also if it was driving a DC generator it would likely to be close coupled and have a shortened crankshaft on one side, or if driving an AC generator it would have had vee belt grooves cut on the flywheel periphery.
The presence of the flat belt pulley is more indicative that it was used to drive a water pump, saw bench, or some other item of agricultural equipment.