Skip & Carla are planning to go that route with their 21! Their boat was owned by Johnson-Kirby, a Miami dealer for the Homelite 4-stroke outboard motors in the 60's. Check out
No. 26 on the home page of Carla's web site! Johnson-Kirby ran it in the offshore powerboat races with twin 55 hp Homelite/Bearcat motors!
Carla may be able to confirm, but as far as I know, they won their class, since I think they were the only guys running 4-stroke outboards!
Although the 21 is a little lighter than the 23 (check the specs on Moesly SeaCraft site), it's the worlds BIGGEST 21 footer! If they could race a 21 with 110 hp with all the fuel they carried (300 gallons?), I would think you would have no problem with 230 hp if you didn't load it down too much. In fact I believe Fr. Frank has said he's rigged 23's new with twin 115's and maybe even twin 85's! However you might need a special prop to plane on 1 engine, something like a 13 3/4 x 15p. What sort of revs do you turn with the 19" prop? I'd think it would be lugging the motor down pretty bad, especially if trying to plane on one engine.