Just a quick update, when I talked to the mechanic (John) at R@E he was quite sure Dennis used or is still using Santana ovalized tandem tubing which from what I hear is nice tubing. Our bike is part of the family and with upgrades over the years still looks terific and rides like jewel. Jmmorford one recommendion I would make is to have the front hub relaced to a 3 or 4 cross pattern. Our White Industries radialy laced front hub self distructed last year on our way back from a ride, I heard the hub shell flange break and fortinuatly was able to get stopped before any damage. Wheelbuilder.com can give you great advise as to wether the Phil hub is subject to failure. The radially hub looks cool but sure if they are meant for the weight of a tandem.
Tandemgeek; your right it's a very cool find, we've only seen a couple of Robins tandems which may explain why he's no longer in business.