This is one of at least 3 General Motors designs made in the late 1960s that feature a Lincoln head obverse. They were originally described as being made of 'powdered metal' but, according to Ken Potter, are actually made of bronze.
Additional information on these can be found in Pollock.
A second Lincoln head design with a different reverse is also available for viewing. We are calling it P4056.
According to Ken Potter, die varieties of this second design exist.
Photo courtesy of Ken Potter.