Hi,
First, the Bailes lock would be fine for an English fowler between 1775 and 1790 or so. For an English fowler between 1760 and 1775 it depends on the quality of the gun. If military, livery, or cheaper export grade, it might have a round-faced lock. If better quality, it would have a flat lock. From 1750 to 1760, good quality guns might have round-faced, slightly round faced, or flat-faced locks except fot military muskets. Prior to 1750, most modest and higher quality guns had round-faced locks.
dave