adding an outboard to the swim platform on a 37 footer

The swim platform is very robust made of 2 inch teak and well attached and supported to the hull.
the boat weighs 17,000 lbs. It is a semi displacement hull 37 footer. waterline length is more like 35 feet.
I was thinking a couple thoughts.

A little gas powered outboard OR

some type of electric AC powered outboard which could get power from my 6500 watt generator.
I think the electric drive is more reliable idea.

Could you get an old outboard leg and put an AC 120 volt electric motor on and how would you control the speed?
How much wattage would it take to push the boat at 3 knots? What HP for the motor? Could the electric motor push the boat at all? 2 knots?, 1 knot?

How much HP gas outboard to push the boat at 3 or 4 or 5 knots? etc...

currently, the boat has twin engines. Running one engine at 1500 rpm pushes the boat to 6 knots. Prop size is around 20 by 21