Years ago, before Shimano produced "flat bar road components," tandem and hybrid manufacturers would combine Rapid Fire shifters with a road crankset and front derailleur. I know that's true because my wife owns a Specialized Crossroads Pro from about 2,000 that came from the factory with LX shifters and brake lever and a Tiagra triple front derailleur. And yes, it indexes just fine thank you. My daughter also owns a Burley tandem, from about the same era, that has similar components but I don't have it available to reference the exact components.