Hmmm, your seatcluster is different form the B&W pic, similar "scoop" to the caps, but yours reminds me of a variation of the popular "Emilio Bozzi" style used on many Italian bikes for decades...yet different, too. Given that the lugs are "Nervex-looking" and the bike came with 27" wheels, I'd guess it's NOT got an Italian threaded BB, true? And if that guess is correct, here's another: Japanese.
Strictly a reckless guess, tho...what's the seatpost size?