Piling on the copper is not the correct way to restore a part. Copper is just a buffer layer for adhesion and ductility. Pile on the copper and you end up with a part that weighs twice as much with distorted flat surfaces, characteristics washed out, and the original defect still apparent.
On pot metal, the pits need to be ground out a filled, usually with silver solder I believe.
Just like in bodywork, get everything as straight and smooth as possible before putting on primer-filler, in the case of plating, copper. That’s the best analogy I can give. Surface prep for plating is a lot like getting ready to paint a car black.
Unfortunately, I used to work in OEM plating (dealing with plastic), but not the resto stuff, so I can't give any good references.