My guess is that it indeed a bicycle pacer, the engine appears French, so the possible venue is the Buffalo Velodrome, Paris. 1907 or thereabouts? Looks like work in progress, no brakes or hand grips for the stoker, no exhaust pipe or fancy bellmouth, for starters. Control rod to the top if the inlet manifold looks like some sort of cam arrangement. The need for a crew of two indicates the engine needed constant manual attention to keep it running, too much hassle for one guy to drive at the same time. Vertical Split Crankcase, tied on rag to catch the oil drips....but a well fabricated frame with a neat finish to all the lugs and joints.
Swarfy.
