It's probably an old IHC horsless buggy engine. They looked very much the same as this (IF this is indeed one of them) Definitly not a compressor. I do beleive i also see the little fan blades on the flywheel. This engine is setting on the flywheel so you can barely see it.
It carry's alot of features that the early IHC buggy engines had. Im not an expert on them but i CAN tell you that much.
I'm voteing for the IHC buggy/truck engine. There was a fellow who had one at the Paducah engine show and the engine ran parallel to the frame with the crankshaft sticking out near the running board. You can see the cross pin in the crankshaft where the crank fit. Not many air compressors I know of with a crank.