I saw an original Hirondelle on Ragbrai a couple years ago. I followed the guy up hill. It's very bizarre to watch. I've been accumulating the parts to make one myself. I just haven't decided on the base bike yet.
FYI, there were 4 speed versions. That's where they used 2 chainrings so you got 2 'forward' gears and 2 'reverse' gears. All 4 of which make you go forward, just at different speeds.
If you wanted to get carried away, try to install 2 freewheels on a SA 3 speed hub or use a Schlumf 2 speed crank.