Peter Green - Green Manalishi, Man of The World, Albatross.
Also, the author and first performer of Black Magic Woman.
If as you say, he played live with Gerry and Duane, I gotta find that.
Google “grateful dead archive by year”
Go to 1970
Go to 2-11
Green plugs into second set Dark Star, but don’t miss Not Fade Away from first set, epic; allman plugs in his guitar somewhere later in Dark Star and there is a complete meltdown through Spanish Jam and Lovelight;