John, some were equippedwith derailleurs. I have a 48 Gillott Road/Path
Tandem which has had a Campagnolo gear hanger brazed on. I have also had a
road/path frame where the dropout had been filed away to take a derailleur.
I also have a rare Huret derailleur with a rear facing slot in the built in
hanger.
I had the filed dropout filled but have decided to leave the tandem as
found as it is part of its history.
Mark Stevens in spooky Evanton Scotland