On average, how many employees would a mid-size New York advertising
agency have in 1960?  What were the job titles, and how many people
would be in each job?

Hello jhlechner-ga,

I haven?t been able to find much about the state of advertising
agencies in the 1960s but in the course of my search I ran across this
site that you might find interesting. Be sure to check out the Top 100
and Top 10 lists as well.

All the best.

~ czh ~

http://www.adage.com/century/index.html
The goal of this "Advertising Century" Web site is to again make the
major sections of that popular 1999 print report available to the
public. By clicking into the items in the upper right hand navigation
bar, you can browse at leisure through the online version of the
"Advertising Century" and learn about our industry's most meaningful
people, events, trends, issues, controversies and advertising
executions.

http://www.adage.com/century/rothenberg.html
THE ADVERTISING CENTURY

I don't know if this is any help, but my uncle worked in a small ad
agency in New York City in 1960.  There were two Account Executives,
one head copywriter, one assistant copywriter, one art director and
two others in the art department (don't remember their titles but they
did drawings and pasteups), one office manager, and one receptionist.
I guess a midsized agency would have more of the same.