Those guns are not designed to handle the extra recoil and abuse that a 338 would dish out to it. I would not attempt it. I'm sure you could find some Joe Blow to do it but I would not shoot it.

A much better bet would be to modify the Weatherby to lighten it up a little. Shorten the bbl, remove material from under the bbl, remove material from under the recoil pad. You could get rid of about a pound from a wooden stock.