kelsey hayes 4 piston caliper rebuild

My .02 cents on the matter.
Don't worry about it.
Sandpaper, emery cloth, Dremel with an abrasive flap wheel, and just go around the bore.
Don't worry about any pit corrosion.
The "seal" is at the top of the bore, and not on the piston itself.
Kelsey Hayes, is a better design than the Bendix, or BUDD, brakes, that the seal is on the piston itself.