Tony, If you are going to visit the Bob Jackson folks, I would see if you can get them to cold-set your frame to 140 or better yet to 145 mm. 145 will open up all sorts of possibilities; Arai drum, or even 8-10 speeds in the future, which would be handy in the Alps. If they feel that 140 is the limit, there should be plenty of hubs threaded for the Arai drum available. If you watch ebay or call some of the US tandem sellers, such as Tandems Ltd or Tandems East, you should be able to round up a drum brake. At 145, you should be able to alternately be able to braze on the stuff you need for a disc brake, leaving the Canti for a back-up. I really think that the Arai, being a true drag brake, is the safer way to go.