Just clean with lacquer thinner, rub off the grease, any of these in good shape, without cracks, or dents should stay with what remains of the nickel plate finish.
Lot of barn car guys want these in that condition. Once the thin nickel is rubbed thru, the brass shows and only the high script FORD type are all brass. Those will sell good, but only in good shape, you can polish the high script FORD caps shiny.