[tahitisail]

John,
I looked into this for my yanmar 2 cyl and figured I only needed to bolt on another water pump and a heat converter and reroute the plumbing to make it work. This wouldn,t keep my exhaust manifold from salting up since I would still be dumping salt water into the hot exhaust gasses.
Looking into the water jacket when I change zincs I see a beautifully clean interior which is excellent for cooling the engine. In fact when I talked to two marine mechanics I was advised to leave well enough alone because the seawater cooling was, according to them, superior to fresh water cooling. Make sure you service your zincs!