Difference is the inlet water temperature. With raw water cooling the front cylinders are are cooled by whatever temperature water the boat is running in. Closed cooling the temperature of the water entering the block is controlled by the thermostat.

So short answer is no set up difference. Thanks all for input.

for marine engines like mild thunder has i add .001 xtra piston to wall clearance.this is for engines that do not use a thermostat.joe,your engines have the xtra .001 piston to wall clearance.

Those vortec motors especially the pcms with the coated pistons run tight ,real tight and seems to survive.
as long as you dont overheat them ..lol seems like i see alot of 180 or degree op tempatures on the scan tool on those though