Yes, that is a bittersweet story. I am glad you found such a nice Farquharson to console your anguish.

I am thinking that the 9.3x74R is the most likely candidate for donor brass. Most (but not all) sources state that the .400/.360 has a base diameter of .470": this is similar to the 9.3. Obviously, a chamber cast, when the rifle is in hand, will tell the story.

Where did you obtain the ammo you used to test fire the Westley Richards?