A chopper or similar. I'm not sure of what kinda lift the 'off the shelf' merc props offer, but I believe they're all relatively neutral.
Again as far as I know, a chopper or yam drag would give bow lift, I'm sure we could find one around 21" pitch. I've got a 23 or 24 pitch one somewhere you're welcome to try though I'd imagine it'd be too tall. The only issue I can see is that they are over hub exhaust, so I don't know if this may give any holeshot issues, it must be a pretty heavy boat so the prop may just act as an egg whisk!
Being able to run with less positive trim will no doubt make a fair difference to top end, obviously ideal is to have the propshaft horizontal.
Thats my 2p, now I'll go see if I can find my chopper
James