Hi daviscfad,
I can definitely understand your thinking on the plating issue.
But I am certain that it is not plated. I have a few
high mint condition 43 Lincoln's and the surface textures
are the same it is just that I believe this particular one
was stored before it came into my possession in some kind
of holder that it reacted with to give it that toning.
I wish I was better at my photography.
Terry