Hi Teo,
You are wasting your time because even swapping out the lock will not change much because the butt stock is already way too small and an authentic lock will be even bigger than the Pedersoli. It will look even more out of proportion with the butt stock than the Pedersoli lock. You cannot make a Pedersoli Bess look authentic. It would be better to wipe out the incorrect "Grice 1762" on the lock and engrave the right markings and leave it at that.
dave