You'll most likely have to do a chamber cast to figure out the correct caliber. Could be almost anything, but this type of rifle was popular in the Hornet, or K Hornet. Maybe even a Mashburn Bee?
The scope is a odd one. Very similar to the JW Fecker, with the center adjustment, but the adjustment isn't built like a Fecker. Maybe it's an earlier Fecker than I have seen.
As Smoke said, the gun is a Stevens 44 1/2 action, with the standard loop lever, and the double set triggers. The 44 1/2 is the strongest action Stevens ever made, and one of the better single shot actions ever made!
Stocks are custom, and appear to be the style used in the WWII-1960's style. Most shooters today go for the more traditional look, but the stocks on that gun wwere made for someone who was a real shooter, and probably a benchrest, or varmint shooter, with that style of stock and buttplate.
It's a real beauty, and probably shoots as good as it looks!