The Shiller Park address indicates the vise was manufactured after 1955-57, which is when Wilton moved to that address. Prior to that, they were marked Chicago.
The bullet vises have a date stamped on the key on the bottom of the ram. Depending on when manufactured, this date is the date of manufacture or five years after the date of manufacture which is when the guarantee expired. My 4-1/2" Wilton is stamped 6-48, which means it was manufactured in 1943, three years later than me.
A short history of Wilton here;
http://junkyardtools.com/tool_history/wilton
