Just picked up a1977 glastron Carlson jet boat with blown motor had basset headers on it before 460 ford motor trying to put back to original state with hardine logs and snails but looks like it?s going to exit under water line  is that ok will this cause any back pressure on motor when starting.or any other issues before I cut the holes for the exhaust through transom .any help much appreciated new boat owner.thanks

So the trumpets are completely submerged yes ?  Thanks for the help Dan need all the input I can get.Appreciate your time.