Which pieces are you talking about? I have a 1971 142; but, recognizing that the grill and headlight treatment is completely different I expect that a lot of the trim pieces are the same.

The grill on the 140 is aluminum and on my 142 E the surround of the grill was polished aluminum with what might have been a clear finish which on my car is history. It might have been anodized. The early 164 grill insert was cast aluminum with the later cars having a molded plastic insert. I know this because I had a friend who briefly owned a 164 and had an oops with the grill. He had an original cast aluminum grill. It has been many years; but, my recollection was that the crumpled aluminum grill did not look chrome-like. It looked very much like the polished aluminum on my 140 which might have had an anodized finish on it.

The molded plastic grills have a chrome like finish on them. At the time of the 164's construction, this was probably a sputtered aluminum finish which was polished to provide a high shine; but, the color is definitely different than chrome.