There are other benefits from duals you would get, like a little better tight area handling, but not too much being close together, and out on a bracket, and if u plane on a single 150 now, its likely u will plane on one 150 offset....what I would check tho, is if the fuel tank has dual feeds, im not sure if u would starve the engines with a t'd single feed fuel outlet...
I think you could also fabricate the full, capped transom with some framing and ply wood, glassed over, and of course a new rub rail....
imo, once you try a 5-10 mile trip home on a kicker, you will realize how excruciatingly painful it is...