Live. Grey Whistle Test?? [Nope, it was recorded at the old Shepherds Bush Empire Theatre, 1971]
"This one is in G if anyone wants to blow along with me. Everybody brought their Marine Band harmonicas??"Bit more; "Heart of Gold from the 1972 album Harvest (a must have -ed.) is Neil Young's only number one hit single in his long musical career. It features the back-up vocals of James Taylor and Linda Ronstadt.
The song is one of a series of soft, acoustic pieces which were written partly as a result of a back injury. Unable to stand for long periods of time, he could not play his electric guitar and so returned to his acoustic guitar, which he could play sitting down.
The song was taped during the initial sessions for Harvest in early 1971 at Quadrafonic Studios in Nashville, Tennessee. Ronstadt and Taylor were in Nashville at the time for an appearance on Johnny Cash's television program, and the album's producer Elliot Mazer arranged for them to sing backup for Young in the studio.
Originally, this song was meant to segue with the song A Man Needs a Maid, and was therefore played on piano. It was played in this manner during Young's solo shows in 1971, but he abandoned this approach midway through the tour and began to play it on guitar as it is now known." -via wikipedia (so treading lightly)
For further reading on Neil check this fantastic older post from JP at TheSelvageYard.