I just bought one of those motors from a friend for $40. I bought parts from bikebug.net. The parts package cost me $160. Was it worth it? I needed a new drive roller, rebuild kit for the fuel pump, New primer bulb, check valve and fuel filter. The literature package was $25, which was a couple of a old manuals and repair guide. I replaced the fuel pump and it still needs some work. Yes, you can definitely machine out a skate board wheel and place it over the drive hub. It would have been worth it if the motor would have just spring back to life, it runs a little rough right now, but I still need some work on the fuel pump. Relatively simple motor and will last forever. Bottom line for me...it turned out to be more a high priced project than I would have liked, and more a "project" than I wanted.
In retrospect, I would have been better to take the $200 I have in it this motor and save the difference for new friction drive kit and motor. I'm contemplating selling my motor, taking a loss and being done with it.