We shouldn't forget the RCV engines either. They have a 60, 90 and a 120 size inline engine.
I think many years ago, circa 1982 or thereabouts a company (RCV?) had come out with a inline engine, but I couldn't get one then. They weren't really selling them in the USA then. I remember reading about them in a magazine at the time. But I thought it was a American company that was making them. I was probably mistaken as it has been a while.
http://www.rcvengines.com/rcv60sp.htm