Gene,
Being that you are really not concourse, almost any 4100 Autolite carburetor with a 1.08 venturi is "proper". However, the part number for a correct one is C5ZF-9500-C or -E. It is identified by a shortened part number stamped into the metal of the left front mounting ear would be C5Z-C or -E. A core would be about $100, a total concourse rebuilt one about $400-500. Sources are here, or e-bay. Depending on where you are, there are Mustang shops or carburetor rebuild shop that might have one.
Jim