The the Scovill Manufacturing Company in Waterbury, CT made the brass dashes. They had a Brass Works division which is probably where the dashes were made. So why would a brass works company stamp a "B" on a brass stamping? Is the the steel mounting bracket for the speedometer different on the brass and metal dashes? I would think the "B" stamp and Scovill logo would have been stamped prior to assembly with the dash panel? They are still in business in GA.
http://www.scovill.com/html/Scovill_About_Us.html