ere's my fear with these and I speak from experience. They are made of zinc diecast which is a very brittle material. If you try to bend it or bend it by accident (like while holding it to a buffer wheel !) it will snap in a heartbeat and repair is virtually impossible on an item that small.

The originals also have a very rough edge around the back which you need to retain for originality.

So if it were me ...

1) I would glass bead each piece myself to remove the black paint (or use paint stripper).
2) I would get a block of wood and drill holes to mount each piece in so that they can be held rigid to work on.
3) I would "sand" them to get the "brushed" finish I want
4) take them to a local plater and say "here, plate 'em - nickel & chrome only".

You'll have to explain why you're doing this. If they try to triple plate you'll lose the brushed finish after the first copper dip - which they always buff before the next step. What you want is just a nickel dip then the chrome and these will leave the "brushed" marks.

Redo the black yourself.