Mike - it is WAY simpler when you don't have to find FI to match the boat's electronics.
I forget the specific thread, but I am under the impression this boat is in the unhappy valley between carbs and modern and available FI componentry.
46Chief - are you sure the intake manifold is that special? Have you taken you old one to someone like an engine shop to see if you could just buy a part from somewhere like Jegs or world industries? You may need adapter and spacer type plates, but I'd be surprised if that manifold isn't darned similar to something somewhere else in the performance engine world.