Kees Koster sends this interesting V4, with double magneto and 2 spark plugs (no one sparkplug; see update below) for each cilinder. Size roughly 600 x 600 x 600 mm. The alloy valvegear covers give a modernish look to the concept. Early twenties? We wouldn't be surprised if it's a boat engine but that's only gut feeling. We gladly leave this all to you experts out there.
update: as Pete Giles remarks, the sparkplugs on the side are only to close the wholes that are water inlets with pipes attached. Still it is a twin ignition with two magneto's, one for each set of two cylinders. So only one sparkplug per cylinder...