Just FYI: Il Vecchio at Leschi in Seattle has a nice 1950 Rene Herse randonneur tandem on display. It appears the bike was modernized (by Herse) in the 1960s or so, with Mafac brakes and Huret Jubilee derailleurs. We weighed the bike, and it comes to only 36 lbs., with fenders, rack and full lighting (but no pedals, so add another 2 lbs. for fully equipped). However, it is a 52/48 cm size split, so a bigger tandem would be a bit heavier!
Jan Heine, Seattle