Treating Rust in Head and Water Passages

[Howler]

I'm at the tail end of a "tear-down" of my 2003 3.0 Mercruiser. Everything looks good and solid however there is a fair amount of rust in the water passages of the head and the block (can see from where the water pump attaches) but there doesn't appear to be any damage. Is there anything I can flush out those passages with that will help try to keep the rust from getting worse and get a few more years of those parts?

Exhaust and risers look just fine.

 

[Scott Danforth]

you could fill the cooling system with oxalic acid and then flush it...... and repeat

 

[Bt Doctur]

could also fill with AF for winter storage instead of leaving it dry