During the 'Delaney & Bonnie & Friends' concert Duane played on a Fender Rosewood Telecaster, owned by Delaney Bramlett, who got it as a present from George Harrison in December 1969 after a 'Delaney & Bonnie & Friends' concert in England.
George Harrison used this guitar during the Beatles' 'Let It Be' sessions and during the 'rooftop' sessions on the Apple building (Saville Row, London, January 30, 1969).
Herbie Mann also played at the 'Delaney & Bonnie & Friends' concert.

"I had sat in one day in Central Park with Bonnie and Delaney, and Duane was playing with them, so I asked if he wanted to work on an album. You never had to say to him how to play the guitar."
~ Herbie Mann

Randy Poe: 'Skydog - The Duane Allman Story', page 149 (Backbeat Books, 2006):

"Delaney & Bonnie’s show took place on August 5, and Duane was there. That night, sitting in his apartment overlooking Central Park, jazz flutist Herbie Mann was so taken by what he was hearing that he made his way to the stage—flute in hand—and joined in. Mann and Allman immediately took to each other musically, improvising solos that stirred the crowd into demanding a number of encores. After the show, Herbie cornered Duane. "I told him I’d love to have him play on my next album. He said, ‘Sure!’ Now some people will call him a rock & roll guitarist, but basically he was a Southern blues improviser," Mann recalled years later. "He was a wonderful player, and he had the kind of feeling that I wanted on my records." (Mann was always open to using innovative guitarists, including Sonny Sharrock—inventor of the "machine gun" guitar solo—who appeared on a number of Mann’s recordings.) It would be almost a year before Duane would be able to make good on his promise to play on an album with Herbie Mann. The road was calling, and there were other sessions to do. But after years of listening to Miles and Trane, Duane looked forward to the opportunity to make a record with a genuine jazz musician.