The key requirement is that the ratchet for the pinion on the top of the crankshaft does not run all the time - it needs to disengage when the pedal has returned to the top of its movement, as it does on an old ATCO. From your first picture it looks as if it would have when it left the factory at least - I'm not sure whether it does now. You'd only have to shorten the chain by one or two links along the way, and the little ratchet would be unhappy.
