too much hrsepower
One option you have is to lower the power of your boat and increase the torque so you still have a nice pull. You do this by changing the camshaft (they go for about $100 and takes one whole morning to do) for one with less valve crossing , this will make the engine idle much nicer and have a nicer response, but it will lower the maximum RPMs and speed. A different intake manifold designed for torque will help too. Then you can show your neighbour that you don't have a stock 351W, but a derated one with a nice low end torque, like a diesel! My pick up truck's engine is like that from factory, it is a similar engine a 1995 GM 350 HD, with lots of low end torque (pulls the boat idling up steep ramps as soon as I let the clutch go like the diesels), but is only rated at 160 hp. Also, if you put a partially discharged battery, and many other accessories, when you go to measure the power at the prop, it will show lower because of all the other stuff stealing power. If it is still not low enough, you can adjust the transmission cable so that the valves don't open all the way when in forward, this will cause the little wet clutches to slip a little when measuring the power.
Please let me know if this helps.
Alejandro
Rebuilding a 1985 Supra Sunsport