Possible Colonial Silver?

This six pence size coin came in during a "Roadshow" style event for ID, brought by a metal detector operator sure he had found some sort of New England silver coin. I believe it could genuinely be of colonial vintage, but could see no under type. So do the counterstamps represent Roman numerals VI and IX meaning "6..9" or perhaps VII and X meaning "7..10," but what then? If anything I could believe this started out as Massachusetts Willow Tree silver six pence and after two hundred years of hard circulation was reduced to this specimen before you. What is it? What was it? Thanks for rendering an opinion, Roadshow style!