After a 2nd look, I see no clutch cable or armature on the outboard motor. It's just a showcase item, nonfunctional, for display only. For all we know, there may not be any pistons or cranks in these motors, just empty cases. I'm disappointed. But from a 'bench racing' standpoint, it does serve as an engineering example for us to discuss how such a contraption MIGHT be made to work.
Map has proposed a possible clutch assembly that could theoretically work. His approach is simple, doable, and not overly complicated. I like it. It would require a custom headstem clamp that wouldn't bind or restrict the pivot action of the handlebars, maybe even incorporate bearings to eliminate binding. The only thing I might add would be a locking mechanism to lock the pivot in place to prevent the clutch from engaging or disengaging from the rider hitting a bump or leaning too far forward. Use a clutch handle to unlock a spring loaded set pin on the armature that grabs the cable ends, with the pin sliding in on one side of the plate locking the handlebars up for fully engaged, and the same pin sliding in the backside of the plate when the bars are pushed down to completely disengage the clutch, kinda like the 'Neutral' button on our kit clutch handle.
Having 3 wheels with 3 individual drive chains is overkill IMHO, that's too much friction. Not to mention the funky handling it would have. Why not just a single wheel riding on a fat 3" or even 4" tire? Or even a dedicated motorcycle rim? Or how about this: A 1000 watt electric hub motor setup for a disc brake from the factory, with the drive sprocket mounted where the disc would go, laced with 12 gauge spokes to a heavy duty dbl wall steel rim? That could serve as a starter for the engines, negating having to pedal or tow the bike up to speed just to start it. If a rear mount A frame or M wave kick stand were used (or even a axle stand rack) you could start it while stationary. We've all heard stories of ragjoints ripping spokes out just from the torque of a single motor, why gamble with that? I also propose a single common output shaft. A custom jackshaft would be the easiest & most simple to craft, using off the shelf componants & requiring the least amount of fabrication or tooling.
But the biggest hurdle I think would be tuning and syncronizing all seven motors to work in concert together. With each motor having its own crankshaft and carburator, uncoupled and in neutral, the disharmonous vibrations of all seven motors running independantly but mounted together on a common frame, would occasionally overlap one another, creating a vicious vibration that will shake like a titty dancer on meth! That could lead to bubbles or foamed fuel in the gas lines, carb bowls & tanks, further adding to the difficulty. To say nothing about rattling loose nuts & bolts, breaking welds & revealing weak stress points in the frame in the form of cracks & fractures.