Thanks for the info and the thumbnail. It was exactly what I was looking for. I did not have much luck finding any info myself on the inet. However, Berlin, Ct is just down the road from New Britain, Ct and I will pass right by there tomorrow. It looks like Corbin Russwin is currently located there. I am going to try to see if there is any archive or museum located there.
The ad you posted suggests 1 grand master with four sub-masters. My guess is that the 53 master is the grand master and the 53C master is one of the four sub-masters (53A to 53D perhaps). The 53 Master is the master shown in the ad and the one shown in the Ilco excerpt.
It is difficult to find anything on the inet like the info you provided. Coincidently, I just found out that my elementary school, built in 1929 is being sold and will most likely be demolilshed. It they sell off the furnishings I will have to get over there to see if there are any good locks like this for sale. Sad to see the building disappear. It is a beautiful old classic school house.