Very nice! I am going to build one myself after I am done with my next randonneuring frame -- mine will be a single speed with angled drops for flip-flopping the hub, though.
The cork helps him go faster! Once upon a time what we now call "blowing up" -- exceeding your anaerobic threshold for too long, resulting in 20 rpm and 4 MPH -- was called "popping your cork". So you simply attach your cork firmly to your bicycle and you will never pop it.