The rocker assembly is the same from '54-'62, on 235 and 261. Sealed Power still makes the assembly. You should be able to get it at the flaps, if not, Patrick's has them. I'm certain that Stovebolt Enine has them, too.
As far as the rust goes, I'm thinking that you mean surface rust on the outside of the block. For that, I've had good results with Por-15 Metal Ready. If ypu use that, make sure to rinse thuroughly, and paint as soon as it's completely dry to prevent re-rusting.
