Looks like it may be nominees for either the Golden Globes or the Emmy’s for 1971. All of these actors had hit shows that year. Still have no idea about the mystery man.
My guess is that it’s Mike Connors, who won the Golden Globe for “Mannix” in 1970. Burnett also won a Golden Globe that year, and Robert Young was nominated. That would have been for the 27th Golden Globe Awards.
I know Connors had darker hair than he appears to have in this photo, but that might just be from the lighting, particularly since he’s sitting right next to the desk.
Looking over the list of nominees, Glen Campbell was up for New Star of the Year, no doubt for his work on True Grit.
I thought there was an issue of this not being the right set for the Tonight Show in 1970, which was much more “modernized”. However, I looked at some footage from 1969, and it’s dead on. The Golden Globes were presented in January, so they probably hadn’t changed to the new set at that point.