Had my ti bike built with a boss for SunTour Superbe DT shifters, the ones on a box on top of the down tube. Love 'em. Bike has always been Campy 9-speed. Used SunTour large cage RDs for the bike's early years, then put on a Campy Mirage touring RD. Love it! Shifting is a good as it gets. (Yes, friction. But I mastered friction as a racer 40 years ago and like riding a bicycle, the skill doesn't leave once acquired.)
(It took me 10 years to learn that the SunTour shifter I picked up at some bike shop used and had that boss made for was a Superbe! Doen't say. I just knew it felt good and shifted well. Looks OK. Saw a photo here and realized what I had. Been a fan of the top mounted DTs since my racing days in the '70s. Yeah, you read that right. I wanted them before they existed because I used to hit the right shifter climbing walls in my 42-19 low. 42-13 on a 20% grade isn't fun!)
Ben