I don’t know why I’m so into this , but you’re right, Peggy
Cass was bigger and more matronly looking. So it’s probably
Polly Bergen, and BOTH of them were on the show for years and years; Dick Clark doesn’t make the cast list for ANY year, so it remains a mystery just who that guy 2nd from left is. But I am on it !
Per one google list, Clark did make one appearance on program: 09/02/58
http://www.ttttontheweb.com/ttttcbspanelists.html
The above had Carson making only one appearance also: 12/05/60
The list at the above link says that it is incomplete, as the program had a daytime and nighttime version.