On September 15, 1976, show 960 of Sesame Street was produced at Reeves Teletape, which then aired on January 14, 1977. Much of the episode involves Big Bird trying to help someone with his broken toy truck.
Update for May 2020: It appears HBO Max has the end credit sequence from show 960.
Update for October 26, 2020: Now Shane Keating, aka Oscarfan, has provided a full guide along with screencaps of the full episode to the Muppet Wiki.