It looks like a Mopar to me. My Chrysler Industrial has an ID plate on the right rear side of the block. Be careful it is an aluminum plate and the paint is easily destroyed. Also on mine there is a plug on the head above one cylinder that when removed allows you to measure the stroke. I think the small hex head near #6 spark plug my be the one on your engine. Be careful to use something that is a lot longer than what you think the stroke is.
