looking at the piks, first its a stepped hull, that will help with speed BUT you have to drive it different or bad things can happen. You need to trim and throttle up to carry the bow in a turn or it can spin. Not a bad thing you just have to learn to drive it different. Then engine, does he have a build sheet?? whats in it? what crank? what heads? valve train, flat tappet or roller? Cam specs? 550 hp out of a marine 454 isn't unheard of or that difficult if good parts are used, however 550 looking at the rigging and condition seems a little questionable. If he made 550 without the right components the engine is going to be an expensive timebomb. When you go and look at it take a deadblow hammer of something and tap everywhere on the transom and stringers. it should sound sharp and solid any dull thuds indicates water intrusion and rot which will be either expensive or a lot of itchy scratchy pain in the butt fiberglass work. The exhaust looks like stainless marine which is good stuff. make sure the starter, alternator and distributor and carb are all marine units.
She agreed to it though. This one still has a stabbin cabin though 
