Looking at that rig does get the juices flowing.
There could be better ways to hook both motors together without all the chain tensioners.
Stack one on top of the other and hack the clutch covers so the chain could fall straight down out of the top one and pick up the near the top of the bottom one and back to the wheel.
I just went down stairs and held one motor over top of another just for fun. Would be a feat to mount them.
I would never attempt to do it but good for them for trying, must be good for clicks and free stuff like a couple new phones to throw in the washing machine.