You might try to find a '57 or '58 elec.start parts motor (bad lower unit, perhaps). If you try AOMCI, look for a '57 starter bracket and starter (take a '58 if offered -- not completely sure about the fit of the '58 bracket, so specify you are working on a '57.) For a simple setup, you will also need an outboard solenoid, a starter button, and an exterior electrical box to mount on the transom -- can get this stuff from a boat store or NAPA, along with wiring. Pretty simple once you do one or two (naturally).