I think a lot would depend
on where your OB bracket is located and what its maximum length of travel is. Some brackets that have a range of 11" - 14" might work on your boat. If you are planning to use a new motor with your existing bracket and in its current location it should be a simple matter to lower it to its lowest setting and then measuring from the underside of the power head (or from the top of the mounting board) 20 inches into the water. I think you would want the prop to be at least 6-8 inches below the waterline. I also think that a 5-6 hp OB would work well on your boat as you don't have open water and high seas to deal with. Some years ago, I had a heavily built 23-ft Alberg Sea Sprite that had a full keel and attached rudder. That boat displaced 3250 lbs (probably +/- 400 lbs more than your boat) and motored well in all conditions with a 5 hp Nissan 2-stroke. I would recommend a 4-stroker these days.