These are excellent locks and would be appropriate for an early Lancaster or other pre-1780 style gun. I have one on my bench and it is really fine, right out of the box. It uses Siler internals and if I am correct, mine was assembled by LC Rice for the Chambers' and fit and function are excellent. I got the one with the Chambers deluxe Golden Age cock and frizzen; just a personal preference; you can get them with the regular Siler cock if you prefer.
Mike Miller uses a lot of them on his rifles and reshapes the pans, bridles and frizzens, etc. Very versatile lock and the curved profile to the bottom of the plate, and slight droop to the tail, give it nice lines.
Guy