How can I upgrade a 3 wire appliance receptacle to a 4 wire receptacle?
Both of the previous answers are completely accurate. New ranges all come with the new four wire plug, however you can convert to a three wire configuration if your box is grounded (in this case your's is) by connecting the ground lug to the box in the female plug. Although this would not meet current code requirements, it is perfectly safe and this three wire configuration has been used for over 50 years before the new 4 wire config was established. This method is a "common sense fix", but the totally proper way would be to run a new 8/3WG Cu or 6/3WG Alu wire to the panel, assuming a 50 Amp breaker is being used.