Remember though, Elmer Keith was a writer and in contact with a lot of enthusiasts and dealers in that time. He was famous for returning correspondance to those who wrote him.
He also bought, sold and traded a lot of guns. In fact, he bought a Westley Richards from my great uncle. I'm not thinking that a rifle passing through the ownership of Keith gives it "provenance". If it had been a favorite of his, hunted with it, wrote about it, then maybe it would be worth 20-50% more, but not more than double the price!