I have a 2001 mountain bike that I am not using. I have considered selling it, but I am interested in buying or building a tandem. Which parts could I reasonable use from the mountain bike. I figure shifters, derailleurs, seat, pedals, and handlebars will work. What about brakes, wheels, cranks, cogs, etc? Has anyone done this? Any suggested references? Any idea where I could get a reasonably priced frame?