No car sitting gets rusted lug studs....ever. Unless they were severely chipped of paint. I have 'never' seen a caliper that rusted that bad, and that includes when I worked on 60's car restoration. Maybe if the car was in an ocean climate and sat for the better part of a year, maybe then the salt in the air would corrode it, but not simply sitting on a lot in LA.

I would look under the car at the suspension and linkage for more rust. If I found some there, I would check to make sure this ride wasn't salvaged along the line.

Now to the post, do NOT paint over that caliper rust issue. If you do the paint will bubble and flake and look horrible in a few months because of the metal. You should really get new calipers, if not, see if you can have the sand blasted or something to remove the rust. I'm almost surprised your pistons can float in that caliper.

My 2 pennies.

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