And I quote Rick "Merle did 90% of it with just a thumb (pick) and first finger. Doc uses the same thing on the banjo, but brings the extra finger in on guitar."
I respectfully disagree if I am correct in assuming you are referencing Doc's fingerpicking. When Doc fingerpicks, he uses the thumb and index finger. No third finger. I have the Smithsonian video put out in the early 90s, with Pete Seeger and a couple of other people, and Doc plays, teaches and breaks down some of his fingerpicking classics. He even tells Pete, he plays in the style of Merle and only uses thumb and index eventhough it's more work."
Unless you know something I don't or I've missed something somewhere.