Power Brake Booster! Black or Plated?

Hey all,
I am trying to find out if the brake booster was black or plated? I am restoring a 73 Dart Sport 340 4spd. It came with power brakes but at some point the booster and master cylinder had been changed out. I scored a great deal on a booster/master cylinder from a 73 swinger with power brakes. It looks to me that it was plated from the factory, but I have seen 73s at car shows that have black boosters and plated boosters. I am trying to get my car correct. So the question is how do I figure out if it was one or the other? Was there a date that it changed from one to the other, does it depend on what facility it was built, etc.? Any help would be greatly appreciated. Thanks.