In ancient times (before the internet!) I used to look at old clock advertisements and catalogs and would try to find a picture of the clock I was working on to determine the missing pendulum or bob style. Now the first thing I do is head for google and put the clock name (Waterbury Clock) into the search field and then click on images. Works almost every time for me for popular clocks. Also suppliers like TimeSavers can often help when giving a good description or maybe passing along a pic.
Hope this helps Marc,