The numbers after the letters are the production order of each series for that plant starting at 1001.
http://www.stovebolt.com/techtips/VIN.htm
Six digits would simply mean they produced more than 99000 units of that series at that plant for the 52' production year.
I am unaware of any list of production totals by plant in 1952. Perhaps someone else has better info.

"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson