It certainly look as if the marking has been filed off the tail of the lockplate. That groove is not something that is seen as a conventional decorative feature. I don't know if it said "Harpers Ferry" but it certainly said something. It isn't French simply because they were not marked with the date as that one is although, as Dan says, early American locks were copied from French ones. Sometimes the only way to tell the difference is that French locks were virtually always marked and American ones, by some of the various early contractors, weren't.
Also, the fact that the armory name has been filed off probably suggests that it was taken/stolen a very long time ago. Long enough ago so that the person who filed the name off suspected he'd be in hot water if caught with it.
What are the proofs on the barrel? It may not be an Ordnance musket at all. Tens of thousands of India pattern "clones," with varying degrees of adherence to the pattern, were made for private sale and a huge number of these came to the US. In fact, with that lock, it is very unlikely that it is an Ordnance gun, much less a modified New Land Pattern.
