Wood,
In about 1988 or '89, during part of the time I was general manager of Advantage boats, we were approached by a couple of guys from OMC. They were trying to shake the bad stigma that the Cobra outdrives got when they were first introduced around '85. They were really crappy and had a ton of problems. The later ones were improved. Anyway these guys wanted to go racing and wanted to know if they supplied the outdrive and engine, would we build and campaign a boat? We chose the 21 Banshee, a little tunnel boat that I believe Harry Christensen (one of Advantages owners) splashed from a Eliminator. OMC wanted a record so we went after the ET II class record in the Kilo. The outdrive was set up with the propshaft even with the bottom of the hull and other than a nose cone and low water pick-up it was stock. The engine was a Mclaren prepped, single carbed, 454 (or 502, I can't remember). We set a new record at, 116 or 118 mph. Broke the old one by about 10 mph. I believe the record still stands today. We ran the Mississippi race twice with the boat and the Parker Enduro once, flipped it in the first turn.
I know that this is nothing close to the set up you have, but I thought you might want to know that these units a pretty tough. I have never owned one but maybe someone else can give you some insight as to how these hold up over the long haul. (the later units) I'd dump some HP in front of it and go for it.