Coop45,A gun writer back in the 60's said the 458 was the best caliber because it was good for everything from squirrels to elephants.. He made us a load that was shot over a wad for squirrels. Damn that sounds good for supper.
I hope you're referring too a pre '64.......... 264wm FTW(Fat Twins Woohoo)!The folks at Wiseman Company south of College Station might help you. They make barrels and their gunsmith did a great job on the trigger of a model 70 I once took there.