Right, the I/O engine (450 lbs or so) is forward of the transom, the transom mount and outdrive probably weigh about 120 lbs. I'd say that you might need a longer trailer to get the tongue weight where it should be. Even though the OB is lighter, it is cantilevered off the rear of the transom especially if it is installed like the boat in the pix with the bracket, that pushes the weight far back, the I/O actually has superior balance.
I donno, if I were in freshwater and trailered a boat, I wouldn't think the payoff of a conversion like this would make sense. Here in the salt pond with most boats being docked or moored, sure it would.
To me the biggest issues with this idea are the unknowns of balance and handling with the engine mounted so far back, and the sheer cost of modern outboards.
You've got a reman 4.3, that can last from 20-30 years if cared for in freshwater, if the engine is clean inside, you could even add a half closed cooling system (longer engine life, and easier winterizing) so with the OB, what's the benefit? At most you could convert it over to a Merc Alpha drive system, if you are tired of hunting for Cobra parts, and a mechanic who can work on them, now that would make sense!
OB conversions make good sense in salt water regions especially the way I use my boat, with it moored in salt water from May to Nov each year. Would I do it? Nope, the most I'd do is what I said above, when the time comes, make my life easier with a reman engine, closed cooling and Merc Alpha conversion. Modern outboards are just too expensive.
