NCJeeper,
Sears didn't begin selling the Atlas shapers and mills until 1953. So the fact that your motor has a Sears nameplate merely means that the OO bought the motor separate, or the motor isn't original to the shaper. Perhaps more likely the former, as the Dunlap name disappeared after about 1943.
The Atlas 7 (and 7A which was the same except no belt guards) first appears in the November 1937 Atlas catalog No, 28.. It last appears in the 1940 catalog No, 40 which was printed in November, 1939. Catalog No, 41 is undated but the shapers listed in it are the 7B and 7AB (no guards). So the probable production life of the 7A was November 1936 through November 1940. So four years. The only serial number that we have for a 7 is 001226. The earliest 7B serial number is 2038. So assume that between 1500 and 2000 Model 7's and 7A's were made. From your serial number (which you did not give), you can calculate roughly when yours was made.