Trying to determine age of Stevens 940E

Question
I just purchased a Stevens 940E single shot 20 Guage shotgun at an auction. I am trying to determine the age of this particular gun with little luck. It is marked Stevens Model 940E, Savage Arms Westfield , Mass. It has 53D in the circle and the underside of the barrel and Firing mechanism are both marked with F D 12. It shoots both 2 3/4 and 3inch shells. These are all of the markings that I have been able to find Thank-You for your time and help!!!

Answer
Hello Tammy.
  Savage Arms moved from Chicopee Falls, Mass. to Westfield, Mass. in 1960 and remained there until it was purchased through bankruptcy in 1990. The Gun Control Act of 1968, required all firearms to be stamped with a serial number. Therefore, your shotgun was manufactured somewhere between 1960 and 1968.
   I hope this helps, and thank you for asking for me. Charles Gage