LarDog,
It is hard to be definitive about these things through photos (and often even with the piece of history in hand), but I think the lock was probably put in the stock as an “upgrade” years ago, possibly in the time of use (likely not later than the very early 20th century). The extra wood cut out for the replacement bar lock looks old (although that can be faked). A photo of the lock mortise beside the back side of the lock might give an indication of recesses in the mortise that were not needed with the new lock, further supporting the idea of a lock replacement. A common reason for replacement would have been to convert from flint to percussion ignition.
The single lock plate screw was sometimes used in flint locks late in their period of use, so the gun could have been made as a late flintlock, but no way to prove it.
Sometimes New England rifles were made with wood ribs under the barrel to hold the ramrod pipes. Yours appears to be metal, but hard to tell from photos. If wood, it is another strong point for New England origin, along with the patch box with a round motif on the finial and no side plates.
Anyway, I like the gun and its mysterious history. Thanks for your ongoing contributions to this thread. Sleuthing out the history of the changing lives of these guns is part of the fun, and changes done during the useful lives add interest In my view.
And Don Stith: Your valuable contributions are in no way “hijacking the thread”. Thanks for the comments.
Bill Paton