I have posted the first photos of my project and as I look at them, it makes me wonder what I was thinking.  Actually, I have tried the turpentine as you suggested and the first go around seemed promising.  Most of the paint is gone, but the dirt and is still pretty strong.  I guess I'll just keep at it a while and find some patience.  In addition to the cartouche, I did find what looks like the remains of a Circle P proof which I didn't expect to see.

I'll post some more "before pictures" later if you'd like.

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