Thanks for the insightful comments -- the lockplate seems to have had an extension braised to the anterior end and the front lock bolt does not even screw into the plate (the hole may have been filled, or braised/welded over) -- thus my idea that the whole plate is a replacement, though with at least part of a fairly early lockplate. What is quite interesting is that I have a Dickert repro lock (I think its L and R) that would fit exactly into the lock mortise, with only a bit of internal wood removal to seat the sear bar (?). I don't plan on doing that, however. The barrel, by the way is held in with flat brass keys and the bow of the triggerguard is an inch wide, the guard and buttplate well filed and finished.