I have been watching Leadbelly on the Vestapol Video "Legends of Blues Guitar Vol 2" and the one thing I can add to what Rick said is that he seems to stay in first position most of the time. At least in the three songs where it his left hand is shown clearly.

Also I have just been told that the "bottleneck" work I mentioned was probably not done with a 12 string; but with a six string on his lap. I imagine he used open tuning for that.

Murray