Rusty,
The engine I have is a truck engine so it has always had antifreeze in it. There is nothing different about the block and head castings between a truck and marine engine. The biggest difference is usually the camshaft.

SB. Yes the block itself is freshwater Cooled. The manifolds/risers (exhaust side) and oil coolers etc are raw water

If you're using it for commercial purposes, and need it on the higher end of reliable, maybe going to a full fresh water cooled system would also benefit you financially in the long run.

Something like a Stainless Marine and appropriate stainless risers.

Relatively easy to find used. If they fail...they leak out...not into the engine.

But if you used them fresh water cooled, they should last indefinitely.

May have to step up the exchanger to deal with the extra BTU transfer.

[QUOTE=Tartilla;4884988]

Fresh water cooled...I would rebuild. You've proven the combo and setup. Changing anything can create unforseen issues during your working season. 2700 hrs on a mild roller cam...it may still be gtg.

​​Have you done a compression test?

If you did one every season when you do plugs, you have a baseline of how it's doing. Maybe just needs a hone and re-ring and clean up the guides and valve job.​​
Merc has a very good handle on engine tolerance specs in the shop manuals.
A Gen VI 1999 Merc I just tore down, with 600 hrs had 4.251" bores and cross hatch.

I agree, rebuild your engine if it checks out ok with the builder,,saves a lot of problems when installing as everything fits the engine bay as originally.

That's the plan as of now. New fuel pumps...manifolds and risers. Oil and transmission coolers and most likely heat exchanger. They have always been freshwater flushed after every use but they are 22 years old. New zf tranny is ordered. Anybody have any recommendations on places to have injectors serviced? Also what's the consensus on the distributor? Any issues using the one I have being its that old?

Send your injectors to Smitty ( articfriends ) on here, he'll do ya right