I think you are correct about CG issues. I think it would be terribly tail heavy as the engine was designed to be up front. You could counter this by extending the nose and stuffing all the radio equipment as far forward as possible. If you look at water planes similar to your idea, like the Northstar and Arrow, you will notice that they have very long noses.

The Outlaw in the picture belongs to a guy by the name of Evan-RCU. He spends a lot of time in the Speed forum too. He's got a cool pic there of an outlaw that he bashed into a twin as well.

Jeff