This is a Pan American 58B. The "Pan American" line of band instruments are Conn's "B" line, and were made by Conn in Elkhart, Indiana. Frequently they were produced for a specific vendor such as Sears. Model numbers usually were something like 40 higher than the Conn model number from which the instrument is derived. Notice the diagonal brace: typical of the 14B and 18B directors. The Conn 14B Director is probably the same as a Pan American 58B. In 1954 (or thereabouts) Conn decided to overhaul its line of instruments and more or less closed the Pan American division and incorporated several instruments including the 58B into the Conn line.