From my collection of off-the-air VHS recordings - Two songs by the Brothers from a televised appearance with the Boston Pops. YouTuber Ken D. checked the Boston Symphony and Pops online archive and informs us that this performance occurred on May 25, 1980. The note in my log indicates that I recorded it from a re-run on August 9, 1981.

The first song performed had been posted before on YouTube. However, I think you'll find this one has somewhat better sound (but not stereo, unfortunately).