I am not sure how much this will help, but I did that conversion on a Yamaha 9.9 about 8-9 years ago when I repowered my Nimble Arctic.  I bought a tiller controlled motor and removed the tiller arm which is where the start and kill switches were mounted.  On the Yamaha, wiring for the tiller arm was easily to disconnect because they had male/female plugs.

Steering was not an issue because on sailboats you  lock the motor and steer with the rudder.  The boat had morse style shift/throttle controls and Yamaha sold a kit for to make that connection.  The hardest part of the electrical connections was to figure out what I needed in terms of switches.  On the Yamaha, the starter engages when the circuit is completed, so I used a momentary push type starter button.  The motor is killed when the kill circuit is broken so I used a push/pull switch there.  WM has lots of these type switches in the catalog. 

Here is some more detail for what it is worth:  http://forum.trailersailor.com/post.php?id=626581&highlight=nimble arctic repower.