I'm confused about the pics of what's what, what's whose, when's that, etc. Lots of pics of different things, which one is the one you have?
My favorite in the pics is the dual matching engines pic post #19 above. Just as much for being unique as for my curiosity about the drivetrains.
I see a single huge axle sprocket, and must assume there's a match for it up close in the pic but hidden behind the left rear tire. Both on what must be a live axle. That's the only facet of the 2 engines that's obviously shared in the pic between the 2 engines.
What else if anything is joined together there, like a single throttle cable, cojoined fuel lines from the tanks, etc? What does it do for braking? If I had a yellow rain suit and a monkey, I could be considered a friend of Curious George, infinitely curious on my own.