Hi Colosus,
A large 920mm hull doesn't 'need' a flexshaft, a solid shaft will work just fine, as long as it's long enough to keep the propshaft angle at a minimum.
The angle doesn't need to be 0°, as these hulls need a bit of propangle to keep the boat on the water.
Check out the Arowana thread here: the yellow and purple boat is the one I set-up:
http://www.rcgroups.com/forums/showt...hlight=arowana
I know, a lot of reading, but a lot of info too on the various ways to set-up a V-hull, both with solid shafts and with a stinger.
The shafts in our Arowana's are 420 mm long.
The shaft needs a few mm clearance when the hull sits flat on the table, like this:
While I'm at it, I assume you've read this one:
http://data.robbe-online.net/robbe_pdf/P1122_1-1067.pdf
Specially the part where it says to flatten the rounded edge at the transom.
As you have a more powerful motor now, the underwater hull needs to be flawless, or you'll experience very 'interesting running charactaristics' when the boat picks up speed, in other words it'll be a bad handling hull.
As a rule of thumb, the front of the prop is 10-13% of the hull length from the transom, which is between 92 and 120 mm in your case.
The rudderblade should sit next to the prop to counteract propwalk as shown in these pics:
Let me know if you need more info.
Regards, Jan.