If it is going to run 65-70mph, I am curious as to why so much pitch at those rpm? Seems to me more disc area (3 blades?) and about 8" pitch would do a better job of pulling a draggy boat faster than a 12-12 at 12k or so rpm. 12" pitch at 12k is a pitch speed way over 100mph - so the blades are running a high AoA all the time at the lower forward speed and may be wasting some energy. Or put another way, I think it would pull harder in the 60-80 speed range. Just a thought.
Man that thing has some hp!