I found this in the Glen L forum and it also has the source below,
"I found the following information regarding cooling the exhaust manifolds.
Coast Guard requires: safety related
There is a distinction for high and low output engines.
In the written part as well exchange of information with reference to an turbo exhaust manifold and its cooling influence relative to engine efficiency.
A marine-specific exhaust manifold must be installed - something completely different from any other application. The
Coast Guard requires the manifold to be heat shielded so that if something flammable comes in contact with it, there's
no fire. This can be accomplished with very expensive insulation (space shuttle tile material) and heat shields. That
improves engine efficiency about 10%
compared to a water jacketed manifold because more heat is available to run the turbocharger. Turbochargers and
exhaust elbows must also be insulated or water jacketed. Again, water jacketing reduces efficiency but may present a
slightly cooler surface for decreased radiated heat to the engine room. Higher output engines absolutely REQUIRE
water jacketed exhaust system parts to absorb the thermal stresses - dry insulated manifolds crack under those
conditions. Needless to say, water jacketed parts in expensive diesels are cooled by the engine's antifreeze/coolant
mixture because sea water is too corrosive.
Source : seaskills / DieselMarinization "
Now, I recon you would be better off with wet exhaust as you already stated you are going stock standard on the motor builld as you will have more than enough power... If you don't want to burn down the house I think wet exhaust is the way to go but I ain't an expert. As for the risers, I recon they could be wrapped up.
I'm not an expert on this so my .02 would be to contact an expert and get their opinion and your options such as TayMC197 suggested http://www.banksmarine.com/
or that oufit I posted on page 1 I think it was.
I want to see it ROLL COAL!!!!!!