I have a Mercury Marine 454, that is from a fresh water boat
Bingo!! The water jackets get eaten up by raw water cooling. We had salt water engines that the flakes wouldn't stop falling out of the water jackets. Every time we turned the block more rust fell on the shop floor. When I worked at the machine shop, unless it was closed cooling systems, boat engines, stayed boat engines.Depends on what you mean by "fresh water". In the marine world that means that the engine itself had antifreeze running through the cooling system. If it had "river water" running through it then it is probably pretty corroded inside and not worth messing with.
Also depends on what damage was done when the rod let loose.
Besides the corrosion potential
If it's from a twin setup - I "think" the right (starboard) engine rotates backwards. do not know how that effects the wear in the engine.
Yeah, the lower unit of the outdrive setup is where the direction is determined to be stardard or counter rotation, not the engine itself.
Aside from corrosion of raw water cooled engines, is there any other reason to stay away from "marine" blocks to put in cars? Big Block marine engines seem to be a dime a dozen in my area.