I had a Zebulon Sheetz rifle that had that same design on the cheek side. I always thought Zeb made the rifle when he was in Indiana after he left here. However, the family who owned the rifle previously said it was in their family since new & they was from WV. I think that is on a few rifles from IL, OH & maybe IN. Kind of rare on a WV rifle.
Frederick Arn is listed in Whiskers WV book. He says he was born in Switzerland. Settled in Pleasnats County 1859. Feb, 1865. Joined the Union Army , Co F ,14Th Infantry. Mustered out in Wheeling June 1865. He drew a pension for disabilty. In 1874 he married Sarah Huffman.
There is more but mostly what you already have. I believe that is the first rifle I ever seen made by him. Thanks for sharing.
Here you go.
http://americanlongrifles.org/forum/index.php?topic=38988.0