Technically the change over should also include neutral switches so it can't be started in gear for safety reasons.
With that said I did it to a 40HP Evinrude and the change over included a new starter, momentary contact switch, and rectifier. Total cost was US $125, but I stock wiring and connectors, and my labor is free. Back to safety there were a few times the boat was started in gear, and I would recommend the neutral switches.
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