Just found this thread (mostly lurk up on the SxS forum, AR and nitroexpress). Anyway, I was the buyer for Frank's WR 318 being discussed.
I won't have the gun in hand for another couple of weeks, but when I do I'll be happy to take some studied pics of the stock inletting, trigger guard bow, etc. I'm as curious as everyone else to see how this all fits together and hasn't managed to tear up the inletting in recoil.
I haven't contacted the Bozeman WR shop, but did request info from the UK--a very nice couple of email exchanges, but I really don't know any more than what has already been said. Sadly, the ledger records were lost in a fire so we can't date it thru them. If I understand correctly however, it may be serial #d at Oberndorf allowing at least a date for production of the action. Concensus seems to point to the 20s though. I picked up a repro catalogue from Cornell Publications (the 1812-1912 Centennial) and they describe it as such on p 104:
"The .318 'Light Model,' with Detachable Stock for Portability. . .In add'n to our ordinary model magazine .318 rifle with fixed barrel or with detachable barrel we now make a Lightweight .318 Magazine Rifle, weighing only about 7 lbs., 5-shot clip loader. Total length of rifle 42.75 inches. Extremely handy for snap shots in hill shooting. Only those experienced in hill shooting or shooting in a hot climate can appreciate the boon that this light rifle confers. The .318 Bore Rifle has been used with conspicuous success in every corner of the world and at all kinds of game. . . This rifle may be had fitted with Lyman Peep Sight on bolt or Flip-up Peep Sight on grip as illustrated. . ."

Cheers,
Bill