Polishing a crank?

The nastiness on the old bearings is probably from acids in the oil. Mmmmm. You could probably get away with 600-grit wet/dry paper and some ATF. I'd suggest something to back the sandpaper (a leather belt that needs to suffer your wrath, etc) to keep the pressure fairly even. That should give a reasonable surface finish. If not, follow that with some psychotic-grit (1600 or something) paper.

Also: beer