At the least you have a Royland Southgate barrel. The 38 caliber is not surprising or unusaual, I have a Southgate pistol in 38 caliber. Your #57 indicates that, at least the barrel, was made and/or marked in 1950. The description you give is not consistant with what he typically built, unless it was done as an order from a client. Even his very plain rifles were in the style of the kentucky Pennsylvania longrifles but with a roman nose butt. Royland lived outside of Franklin Tenn on a farm called Rebel Hill and died around 1979 +/-. He had a brother, B.W. Southgate who also built a few guns and lived in Inglewood Tenn, near Nashville. Southgate rifles and pistols are very collectible and some of them fetch some handsome prices. Hope this helps a little. I thought about it a little more and perhaps you have a B.W. Southgate rifle. Royland usually only put an R before his name but Bailey used BW.
Mark