I have used this forum to try and provide a solution on my ribcraft 5.3. The overall concensus for my size boat seemed to be 4hp as an auxillary, and 2 stroke so it could lie on the cockpit sole when not needed. I didn't want it "usually" attached to a bracket due to the poundint it would receive. The other problem I had was the A frame in the way.
I bought a s/hand Tohatsu 2stroke 4hp longshaft and I fabricated a mount from 5mm 316 stainless with an iroko mounting board.
See the photos (a little dark, taken on February evening).
Only now need to see the result in anger....