Charlie P. (NY) said:
Dozer Dan - what are the initial under the crown? English military locks were marked "GR" for Fat George (Georgvs Rex) from 1760 to 1820 or so. The name on the tail of the sideplate is the lock maker. "Tower" was most common (Tower of London) but Grice, Ketland, and others pop up.
The serpentine plate opposit the lock doesn't look quite English, but that's just a personal opinion.
Also note - locks were sold seperately and often reused. It may or may not date the rest of the pistol.