Looking at the first photo, I also picked it as an air compressor but I would like to suggest that Art's suggestion that it would run rough may be mistaken (and I know this from first hand knowledge based on the following).
My father converted a Y-block 272 (in an early Ford PU) into a V-4 by removing four pistons/rods, covering the oil journals to ensure proper oil flow and changing the carb so the engine didn't get overfed. I drove it once or twice for many miles...it was very slow to get moving and it sounded a bit like a model-T but it got great gas mileage. and it idled and ran smooth.
They may have increased the weight o the flywheel in the flat-head driven compressors to smooth out the power pulses but I bet it ran smooth.