Hi Cyten. Congratulations. That un-decorated gun looks like it would be a perfect candidate to make into a shooter.
As long as the rifling isn't chipped or gouged it should work fine. Those Ottoman barrels are heavy and thick at the breech. And the thread integrity of the breech plugs are usually well done. I've noticed that the 8 groove rifling is the most common I have encountered on these barrels. Would be interesting to see how accurate the original rifling is. I hope you decide to go ahead with this. What condition is the lock in ?
Slings: Yes, the round rings are likely a 20th Century addition. But they look good on that gun. LOL Originally, the two slots for a leather sling would simply accommodate a single piece of leather entering the left side of the slots, and simply knotted on the right side. What's interesting is the style of knot. Somewhere, I have a photo of an original sling knot. I'll post it here as soon as I locate it.
The brass cap covering the tang is a common feature on many of them. Often, the barrels had very thin linen in the channel that was coated with some kind of wax to act as a form of glass bedding. (Found this on my Albanian gun).
About the shorter butt stocks found on some of these Ottoman long guns: Yes, there has been some debate about this with some collectors. It is my opinion that all the guns with the short butt stocks like Hawkeye's originally had a rear section - that is simply missing. They were held together with one or two large, long nails, and typically with the center band. Also, with the occasional exception, the stocks were made without butt plates. Any brass, iron, leather, etc. on the butt end is likely a 20th Century addition from someone who simply doesn't know.
But it sounds like it would not take much work to restore her to shooting condition. Keep us informed if you do.
By the way, the long guns with rifled barrels are called a Shishana. The same gun with a smooth bore a Tufuk.
Rick