I though the alloy wheels used on the Beaufighter were the same Avon Safety wheels that were available as an option for the 411 S5 and the 412?

You could phone Brian Marelli at Bristol Cars Services - ask him if (a) he has any secondhand nuts and washers for the Avon Safety wheels, and (b) if they will can be used on the Britannia wheels.

He will of course suggest you buy the SS nuts that they now use.

No they are totally different Wheels on the later Britannia/Beaufighter than the 411/412

replace studs
 

Is there a reason why one would not be better off selecting a standard modern stud, rethread the wheel to hold it, and simply switch to an off-the-shelf wheel nut?

I have new wheel nuts available if anyone needs them - the 6 cylinder are the same thread as the V8