A couple of thoughts. My guess is that going from an inboard to an outboard is actually quite a project. I take it you intend to remove the old engine and tank? This will, of course, effect the weight of the boat and also its balance as, im guessing, it was designed with the assumption that it would carry an inboard. Also, I dont believe you can just slap on outboard mount on the transom and mount an outboard to it; I would imagine that the hull needs to be reinforced in that area both due to the weight of the engine and the force it will exert on the hull. I agree with the posts above regarding a long shaft; typically you want that prop as low in the water as possible so it is driving as often as possible. You have two basic choices in outboard: 2 cycles and 4 cycles. Each has its own advantages and disadvantages. 2 cycles require a gas/oil mix and 4 cycles drink pure has. Typically 2 cycle engines are cheaper in initial cost, less efficient than 4 cycles, more polluting than 4 cycles and lighter than 4 cycles which can be a big advantage on, say, a dingy engine. 4 cycles typically are more costly, less polluting, more efficient, and have better life. Ive had many of the engines you listed above. My favorite was the Honda engines that I have owned; they are expensive but worth it in my opinion as they offer a long life and are relatively easy to maintain. I currently have a Nissan 9.8 which is the lightest engine I cud find in its power range as I need to take it on and off my dingy with some regularity. I would suggest talking to a marine engineer or surveyor before walking down this path. Good Luck.