Hi Rich,
I think I can give you a pretty precise ID except I suspect the lock was repurposed and used on some later civilian gun. I believe it matches the heavy first version of the French model 1763 musket. The locks on those were originally about 6 3/4" long. Troops complained about their weight and the model was very quickly modified by shortening the lock, lightening the barrels and stocks. The lighter version became what some identify as the models 1766 and 1768 muskets, which many folks in America incorrectly call the "Charleville" musket used in the AWI. It just so happens the Charleville armory made a large proportion of the surplus muskets sent to us by the French. Probably most model 1763s, 1766s, and 1768s produced were made at St. Etienne. TRS should have all the missing components but make sure you order their parts for series 765, the heavy model 1763.
dave