Yeah, having looked further into this it'd seem that sticking with the two props may be the answer for a variety of reasons including the above.
I'm getting mixed opinions on working the props to reduce blade area etc, as duo-props are such a fine art that many don't understand fully. I can see that if they're not working perfectly in unison then the drive will just try to rip itself apart.

Now I need to decide on my x-dimension. My current bravo is pretty high and I know the propshaft to input shaft length is near enough the same on the two drives. I've seen a figure of cavitation plate 35mm (about 1.5") above bottom mentioned. I can always add a spacer if required but would like to keep the motor as low as possible

James

hello find you a solution to your dpx? I want to put on a sportsmaster in the house,must find more speed for the boat