I use scotchbrite pads on an air powered die-grinder to prep the exposed metal/corrosion, light sanding over the old paint. Zinc chromate the exposed metal, and then coat everything with black engine enamel.

Sanding sponges work good on the tough areas too.

Lots of good stuff here but a couple more ideas, after you blast or sand you must Zinc Chromate right away because the case will start to oxidize immediately. Use a good epoxy primer, key word being epoxy. If you need to use filler shoot primer first then prime over. when you shoot the Zinc Chromate go with a very light coat, you are using it as an etch not a coat. Do not skimp by the good stuff or you will do this next year to.

I did mine 5 years ago cleaned it up sanded rough spots and sprayed it with rustoleam gloss black Still looks ok and touch ups are simple. The boat is on a lift so it isnt in the water all the time