I'm skeptical that it'll get on plane at all. I've had a hard enough time getting some boats on plane, and that was without a 4cyl in the front. Do you use it that often in the water, and on that big of water?I'm going the route of a big trolling motor on a bass boat retractable mount on the side of mine and just going to live with the slow water speeds. My idea is that I'll only use it in the water long enough to get me to somewhere my wheels can bite.
Be careful removing the tires and using it in the water as the tires add a lot of buoyancy and stability. Even if it is just a test, I wouldn't want to hear that you to accidentally capsized it.