Actually it's none of those, take a look at the google sketchup 3D library, I uploaded it as the Sanko Engine, if you're interested. It is simple like a 2 stroke (no moving valves or camshafts), and it is also a diesel, so no spark plugs either. It is a boxer configuration with 4 cylinders but that doesn't tell the whole story. I'd like to make it out of aluminum. I will export some 2D drawings and post them.

Thanks for the response.