take a look at how Paketa sets up their one sided drive trains.
If you can use a belt, the lightest setup is likely to be a single side drive, with a 2x10 (or 11), and the belt in place of the third ring.
You might need to run the belt on the outside of the crankset for chainstay clearence.
Paketa Custom Magnesium Bicycles :: V2r Superlight Racing Tandem Bicycle with Gates Carbon Belt Drive:: Best in show NAHBS best alternative material
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.