OK, this thread is now about how to build a fixed gear Corsa.
First obvious problem is you have to pedal backwards to shift on a conventional corsa, but that's because the changing mechanism is on the top of the cassette. It's not inconceivable to move the changing mechanism to the bottom, so you can shift when pedaling forward, right?
Hey, if you run it down the back of the seat-stay, it should work out perfectly.