A Griffon ?! I can imagine how glorious that thing sounded - big Merlin & Griffon fan, and I miss the "proper" engines in the hydros.
A buddy/mentor & I ran a couple tunnel-hulls back in the late '70s, and yeah, the blow-overs were something you'd think about.
Lots of finger-dancing on the outdrive controls to keep the thing on plane; you could feel the boat getting light and the hear the RPM & prop speed pick up when the thing was about to swap genres, so to speak.
Couple years of that and we went back to things with tires...