I had continued my contact with the seller, providing him with some information gleaned from this forum. Here is part of his last reply which I received this morning:
"
Hello, my grandfathers friend a man by the name of
Sherman McCalister told my grandfather that he
obtained the plate directly from the railroad. My
grandfather looked in his records and my
grandfather bought the plate from him for $5 in
the early 1960's. (Yes he still had the record of
it lol.)
My grandfather is now questioning if his friend
really got it from the railroad like he said
though, and we're starting to think it is one of
the stolen plates. We're contacting Durango &
Silverton Monday. I updated the listing. There is
some mystery to this plate I agree, but I believe
100% it did come off a locomotive and it's not a
replica. Based on the serial number I would have
to believe it came off of the 482 despite the
casting number debate.
I do have another narrow gauge plate sitting
behind me from Great Northern and that does have
1/4 E in the casting number. You're the first
person to message me with some real info that made
sense and not just accusations. Thank you for
that."
Seems like he is interested in doing the right thing. Now if we just knew who Sherman McCalister was.