I regret I can't offer any help on your search, but this might help you figure out some of his songs. When I saw him in concert, I learned a nifty little variation to drop D tuning. Instead of dropping the low E to a D, He put a Shubb capo on the second fret covering only the five bottom strings and finger picked several tunes in that tuning. I guess that would be called a capo'd open E string tuning. I play around with it and find it a nice change and requires a minimal re-tuning effort.
Mudjack