Water jacket - How clean is clean enough?

[Yoyodyne]

I finally found a good 21 stud block to build and am cleaning it up to prepare for machining. Here are 2 photos of the interior of the water jackets. Is there anything to be gained in cooling by cleaning the last of the rust from the surfaces? I imagine that if I do, it will just rust again eventually. I don't have a Redi-Strip within driving distance any more, so I'd have to ship it somewhere to get it derusted, but I have a year and a half plus lots of effort and money disassembling and cleaning motors just to find this one good block, and don't want to short cut the prep.

The photos look more brown than the block looks to the naked eye, I think that's from the flash. The first photo is inside the block between the 2 center cylinders.

What say you more experienced guys?