Minimum HP to make your dinghy 'plane' with two persons (340lb.) will be approx. 8 HP, ~6HP if only one person (170lb.)
2 HP will 'move' such a dink around 'nicely'.
The probable 'best' 2 Hp OB ever made was the 2HP, 2-stroke Evinrude or Johnson from the 1970-80s .... and you still see them on Ebay. And such still have active parts availability from Bombardier Industries and their parts distributors. Weight is about 15 lb. easy to maintain/fix.