The first drive I would look at is the Weismann. Fifteen years ago they dry-sumped Mercury's #6, then designed and built their own. It's half the weight of the Merc and is rated @1600hp. They are also testing a new version of the old Blackhawk twin prop drive also [email protected] Their drives and transmissions have been banned from US Offshore racing because they were TOO good, i.e. giving Merc too much competition.
Give Pat Weismann a call, see what he can do for you;