The full octagon barrel, grip shape, and long foreend are not right for any Remington Rolling Block pistol I have seen pictured.
I think it is a cut down rifle, which is illegal under the letter of the law but not likely to bring in BATFE SWAT... I hope. But then I recall the article about the nicely done pump action pistol built from an 1890 Winchester that was confiscated by the feds.