If the pits are too deep to file the surrounding metal down to the depth of the pits, which would obviously destroy the scroll work you mention, and may compromise the strength of the receiver. The other option would be to bead blast the receiver and then parkerize it, or paint it. If the pits are very bad I am afraid the scroll work is going to be sacrificed. Only other thought is to cold blue the pits, dirty way to color the metal and camouflage the damage