if your b&w have the top mounted tweeter, I would highly advise against shipping them without the specifically molded B&W packaging materials...
call the North America group up in MA (978) 664 2870. They can let you know if they have the boxes. Yes, they are expensive - boxes for some N804 I used to have were something like $150 for the pair. But if you really want to ship the speakers and want them to survive, it will save a lot of headaches.