The zz4 is not designed to be a marine motor. It does not have the correct cam, bearing or piston clearance. I'm not sure, but it may not have forged pistons. This would not be my first choice for a marine engine. That said, I'd guess that it'll be quieter than the V-6. The 4.3's really rap. Yes, you can move the tips below the water line. Be sure to use a good flapper and have some extra rise to the system before turning down.