Thanks for the nice replies everyone. I did end up sharing this find with the dealer I got it from. It happened to be a dealer that I do a lot of business with and I'm just not the kind of person to keep secrets like that I guess. Also, if I was in their shoes I figured I would probably want to know as well. The coin somehow got misplaced and ended up in the foreign bin. I do believe it is a dug coin that has been very nicely cleaned. Because I'm already doing a type set, and because it is a scarce variety (Sheldon 63 was my thought as well) I actually already sent it in to NGC. I intend to hold onto this thing for a long time even though it's gonna be a details grade.
The pictures don't quite do it justice, partially because I'm bad at photographing coins with my phone. The corrosion is obviously pretty bad but there is definitely some meat on the bust. I think it has a shot at F to VF details which the dealer (who is a solid grader) agreed with.
It definitely has my blood boiling to get out and do some detecting too, because you never know when you might find something like this in the ground.