This 1660 lock is very rare and quite early. Its a big old lock, 7¾ inches long, unsigned and I bought it in Florence some years ago. It has a strange sear arrangement and what amounts to 3 separate sears all acting horizontally 2 of which work through the lockplate to provide half and full cock - hope that makes sense. The frizzen face is detachable and held in position with a small screw. I've attached some more photos of the lock that should explain things.
Copy and photos supplied by Brian Godwin.