Here's 'Get Back'. If you look at the people in orange t-shirts closely, you'll see the Welling choir in the back 4 rows!
Here's Ellie's solo in 'Let It Be', sung with Kway of 'I'd Do Anything' fame. At this point in the concert, a drama of John Lennon being shot had just been played out and the lights went out as he was shot... then all the performers lit a torch and the pair begin to sing. Spine-tingling stuff, I think you'll agree!