"The 70hp merc I have has been worked over a fair bit," he says. "Custom built head. Modified front case to have 3 carbs. Light weight flywheel. Nose coned gearcase with low water pickup. Im pretty sure the motor will run this boat into low 80's."
"Dad has a 12x21 overhub cleaver he swears will work, but I dont know. He is a racer from way back running champ boats."
I'd say that prop would be an excellent place to start.