As long as the manifolds are cooled by raw water, fresh or salt, they will be susceptible to some degree of corrosion. The only way to eliminate the danger of rust is to cool them with the engines coolant loop.
I have replumbed some Perkins motors to accomplish that, it worked out well at moderate throttle settings, but temps would creep up at WOT.
It’s dependant on the capacity of the heat exchanger and it’s piping.
You’d have to do some homework on your particular engines specifications to determine if they could safely handle the additional BTUs.
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