I saw this caliber in a old guns and ammo annual the gun was built for Elmer Keith and I have a Hagn action setting in the Vault and I am interested in building a gun in this caliber

One of the Wolfe Publishing compendiums has an article on it. They might be able to sell you just the back issue as well.

I rebarreled a Ruger #1 in 338x74K. It turned out great! I love the 4"+OAL w/ 250gr bullets. It basically runs like a 338winmag from a flanged case. If you get one put together, drop a note & I can get you some starting load data.
Clymer did the reamer for me & the throat is on the long side, which helps w/ pressures, but can play havoc w/ accuracy w/ shorter bullets.