Hi,
Flat faced locks on English guns started to become popular on higher quality guns in the 1760s. However, that usually did not include the bells and whistles such as roller frizzens, "waterproof" pans, and such. Those became popular in the late 1770s and early 1780s. There were some early roller frizzens in the 1760s and early 1770s by William Bailes (not the Bailes the lock is named for) and John Twigg but they were not common. The L&R "Bailes" lock, which is also called the small "Manton" lock is appropriate for guns during the late 1770s through the early 19th century. The Chamber's late Ketland is more of a 1780s and later lock. These locks would start showing up in the colonies during the late 1780s after the Rev War was over and imports from England began to flow again.
dave