That is an extremely long example. Jamestown rifle makers did take in special orders. I found a letter where a man in Louisiana ordered a Longrifle from Jay Lamb with a 52 inch barrel to use in Match shoots.
If this rifle is signed by Obed M. Dixon it is the only full stock Longrifle that I have seen by him or heard of. He was born in 1828. In the 1850 Guilford Census he was living with and working for gun smith William Lamb. In the 1860 census he was living beside Anderson Lamb on Mackay Road in Jamestown.
Over the years I have owned four of his Longrifles and still have the best one along with a Jamestown Bullet Mold with his name stamped on it.
Here are some photos of my Longrifle by him.
Here is a photo of the Jamestown bullet mold signed by him.
Thanks,
Michael