The basses would not necessarily have been gut, Martyn...but you might be right about the octaves. They would still work, musically, as bass lines. Can't see the point of it though. Maybe there was a difference between strings for the theorboed guitar shape and the archguitar lute shape?
Rob -- To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html