For a carb, I run a Holley Marine 750 w/mechanical secondaries. With a jetboat, you'll want mechanicals as opposed to vacuum. As long as your cam is stock or mild, a 750 should suffice. As for an intake, again, with a mild cam, you could getaway with an Edelbrock Performer. I think they are good from 1500-5500 rpm. If you bump up the cam at all, I would go with a Torker Manifold (single plane)