Gary,
I see your point, but I think I'll stay on the other side of the fence on this one.
I think the original lock had a rounded tail and a rounded nose, like a percussion of that period likely would have had.
If you consider that the overall architecture of the gun is nicely done, my thoughts are why would the maker go to that trouble, then fit an ill fitting lock to the gun.
As Dennis points out, the nose of the lock leaves little wood surrounding it, yet the maker left ample wood under the bottom line of the lock plate, so why not around the nose.
I think the reason the tail of the lock fits well, is because the wood had to be cut away from where the original round tail lock mortise ended, so was decently cut away to fit this pointy tail lock.
And the biggest question for me, if the lock was original, and considering the overall workmanship of the gun, why would the maker make the lock plate to drum fit so unbelievably ill fitting.
I can't believe that the guy that inlet and engraved the patchbox, is the same guy that fitted this lock.
Probably the only Maybe surefire way to know for sure, would be to pull out the lock and examine the wood under it.
And of course. I've been wrong before!
John