To my eye that appears to be a rather old homebuilt engine. It is certainly missing the valve linkage, has at least one loose bolt on the cylinder endcap and will definitely be wanting new gasket seals on the cylinder. Not sure if it is missing an eccentric on the crankshaft for driving the valve rod, or if it is on the far side of the pulley wheel as the valve crank arm seems to suggest, which would be a rather inconvenient place for it to be, but could still work.
BTW ..... WELCOME to the Forum. Truly hope you get your questions answered and succeed in bringing that interesting old heirloom back to life ...... then get seriously hooked on steam as an interest and hang around here for a long time to come!!! ;c)