Nigel,
We have some reluctance about rebuilding our Trek T900. New Orleans does not have a bike shop that specializes in tandem bikes. We use one of the premier bike shops owned and run by a guy who has a lot of experience (but not with tandems). When we get our bike back after work has been done on it, sometimes it is fine and sometimes not so fine. We're having a hard time with the idea of putting out a lot of cash in the hope that our local bike shop will get a rebuild right. If we lived where there is a shop specializing in tandems, we might feel differently.
Apart from that, I think the learning curve would be too great for us to figure out what components we would want. I have spent a lot of time researching models and features trying to figure out what would be a good fit for us. The input from this forum has helped a good deal. The next thing I will research is "a 559 rimmed tandem that is capable of accepting 58-622 tires (larger OD than 28-622") from your reply. I think it would take me forever to go through all components on a tandem bike sufficiently to know what we want.