Just to clarify things a bit...The further the exhaust/engine coolant water mixes with the engine exhaust the better. Really has no bearing on where the water exits around the water line.

The valve cover gasket I referred to as 'double' is not two gaskets stacked on top of each other. Rather it is just shy of twice the normal valve cover gasket thickness. This allows the interior top side of the valve cover to clear the poly locks on roller rocker assemblies. Typically taller valve covers will interfere with marine exhaust on small blocks. Not in all cases, but many. We are simply giving you proven options from working configurations.

The internal stiffening and oil breather baffles may need to be trimmed if using stock valve covers and roller rockers. However I found that the internal bracing on stock Merc covers will slide between full rockers, and the oil breather baffle just needs to be squeezed/pinched a little with your fingers and it will fit between the trunions on installation. Once they clear the trunion pivot centerline there is no clearance issue. Kind of confusing I know.