Hi Eftihis.
Nice find indeed !! What an interesting wall-sized gun. It does seem the barrel from an earlier matchlock was re-used with a later stock and miquelet lock added. The re-use of older barrels being fairly common. And this would be a good example. And likely Balkan made as Oliver suggests. The interesting features I notice on this gun:
Barrel: While the so called tulip style muzzle would add strength to help prevent muzzle damage, I believe was mostly a styling exercise. You can see the two grooves on the muzzle of your barrel where the twin blades of the front sight once resided, like the barrel from the museum. The twin blade front sight picture seems fairly common on early Persian made barrels (see photo below).It's a beautiful barrel with some wonderful chisel work.
Stock: The butt stock is styled similar to a Dzefeder long gun. Which just adds to it's likely Balkan origins. What is interesting is the barrel is held to the stock with pins versus the typical barrel bands. This suggests that the older barrel was fastened to it's older original stock with pins. Thus the pin fastening method was re-utilized in making the gun in it's existing configuration. Just a theory. The barrel could be considerably older than the stock/lock. The ring on the rear, left side of the stock suggests there may have been an arrangement for some type of carrying sling. Possibly another ring or other devise towards the muzzle end, now missing. It does seem the forend of the stock may have beed cut back sometime during the period. Possibly due to damage. As the ramrod would be too short to load with.
Lock: The larger proportions of this miquelet lock tells me it was made for this gun. Or at least a wall-sized gun. The long, narrow jaws of the hammer and the pan area lacking a fence, remind me of Circassian styled locks. But I'm sure it's Balkan made. The simple, yet decorative file work on the lock is interesting. The longer support arm giving away the larger than normal size of the lock.
Again, a really nice find. Another gun I wish I had seen first. LOL
Congratulations.
Rick