Hello francois and congratulations on a great find. You have a French M1728 musket, basically. All is as issued except the buttplate (not shown), lockplate, frizzen, frizzen spring, pan, rear swivel, and middle band(missing), to which the top swivel was attached. Contemporary restocking in maple,
probably by an American maker, which could date the work as late as Rev. War. Hard to date the lock work without examination, but as it is not
the original M1728 lockplate, the exterior components could in fact be original to the present plate. Condition appears better than average for this
type piece, you found it at a great location, and overall is a desirable gun and would be a welcome addition to a F&I or Rev. War collection.