digitalfreaknyc said:

I'm betting most people have never seen this before...
It was filmed September 12, 1978 at Fox studios.

https://www.youtube.com/watch?v=buRGuDX8Oek

It's....quite somethin'.

It wasn't for the Holiday Special. It was filmed for the dance number as part of an entertainment program at the time. There was a video online years ago which had part of the program either side of the video, but i can't seem to find it. The only one i could find was posted in 2010, although edited to remove the segment of the show, but you can still hear the clapping at the end.

https://youtu.be/yO82BzjPvFc