High quality repro of the Sox & Martin's Plymouth Supercar Clinic "Plymouth's Winning Beat goes on!" license plate as seen on Ronnie Sox's Super Stock Barracuda.  Printed on aluminum in SC, USA by veteran and woman owned company.  
Sox and Martin's Supercar clinic in 1968 and 1969 featured the race cars and info on how to modify your GTX, Road Runner, Barracuda, Hemi for NHRA stock and super stock Drag Racing.  These license plates were given out as door prizes.
They promoted Hurst Performance Shifters, Keystone Wheels, Fram, Stewart Warner, Good Year Tires, Valvoline Oil, Champion Spark Plugs, Edelbrock Manifolds, Hooker Headers, etc.  273, 340, 383, 440, 426 wedge and hemi engines.