Bill Staines had a "horn concerto" that he did with his mouth---immitating a french horn---while doing a very fine guitar backup on his steel string guitar. He never recorded it that I know of---although I do have a concert recording with it on there that I picked up from Public Radio some 20 years ago---back when they still had folk music and were truly "public" radio. It was wonderful.

But Bill plays guitar upside-down/left-handed so I was never able to figure out what key or whatever he was picking it in.

Elizabeth Cotton also played upside-down. Her biggest problem was keeping her skirt down. ;-)

Art Thieme