Gauge Panel

At TR4 body 4399CT the dashboard panel for the 4 minor gauges changed from polished aluminum to black painted steel. While looking for something else in my inventory, I found I have 2 of the polished aluminum ones and another aluminum one that was painted black. My initial thought was that it was painted by a previous owner. But if so, he really knew how to prep and paint. It appears to have been baked on because it is very hard and almost impossible to remove. I tried a small patch on the reverse side.

Perhaps someone with a little more experience or insight can give me an answer. Was this likely a modification of a previous owner or was there a transition period between the aluminum and steel panels where this was done at the factory?

Gary