OK. Thanks Flint and Rudyard. The reason I asked for a guess at approximate year you think the gun was made by Kit: I seem to recall that sometime during the 1980's and maybe stretching into the 1990's, there was a growing interest in replica arms that could be made to reflect patterns from say pre-1650 or so. And I don't think The Rifle Shoppe opened for business till around 1990 there about. So it would seem that during that time a matchlock like the one posted here was considered a one-off type of item created by the builder. Barrels and wood would have been available. But locks and other hardware would have to be made from scratch or improvised from something else to create the finished gun. Per the OP's post, cutting off have of the percussion bolster and welding on a hand-made pan and cover is a good example of this ingenuity.
Here is another example of one of these unique builds that I picked up at one of the annual Baltimore Antique Arms Show a few years back. Appears the attempt was to make a mid-17th century dog lock style fowler. The hardware looks all hand-made. But the lock is what is so interesting. It obviously started life as a Siler lock from Jim Chambers using what he calls a "Builders" lock. Being that the lock was assembled, but the plate left square so the builder could contour the plate in any desired fashion. Then, a dog-style safety catch was added, with a slot cut into the hammer, and a hammer stop added to the lock plate. Even a lock plate screw added to make it an earlier style three-screw lock.
View attachment 185418View attachment 185419View attachment 185420Of course the safety notch was on the tumbler, so the catch and stop additions were primarily just for show. The gun was unmarked anywhere. And all that was needed was a through cleaning to put it in shooting order. It would be good to know when Jim Chambers first started offering his "Builders" lock. That might be a clue as to when it was made (?) Later on, I decided that the lock looked a bit on the smallish side compared to the overall profile of the gun. And thought this would be another one way down the list to refurbish. So I sold it to a fellow Forum member. But the lock does show the ingenuity in trying to duplicate an earlier gun using whatever was available at the time.
During the last 3-4 years, these less common type of custom guns have been showing up at auctions or otherwise offered for sale. I'm guessing that original owners who are aging or have passed away and have no off-spring with any interest. Anyway, here is a couple pics of that gun I saved:
(as a side note, I notice custom long guns and plains rifles from the 1970's and 80's showing up for sale everywhere)
Rick