Probably need to replace the piston ring too.  Sounds like the old ring is stuck.  Putting the piston in the hot/warm anti freeze over night may loosen it up.  Otherwise, get a replacement.  If you replace it make sure the ring groove is cleaned out well.  So if you replace the bearings, you might as well replace the ring.

I have used jeweler's rouge and a buffing wheel to clean up crankshafts.  I would not use any emory cloth at all, the rouge is much finer and will not remove gobs of material to get the surface rust off. But otherwise, like others have said, unless the rust interferes, I would just leave it alone.