You will probably need more than just his name and dates of enlistment/death. I checked the National Archives WWII casualty database (available online) for a John J. Kelleher in New York County, New York, and found this listing: John J. Kelleher, serial number 32895062, rank Private, Killed in Action.
If this is him, you might have the wrong enlistment date. The Archives WWII enlistment database shows this serial number assigned to John J. Kelleher from New York County, NY, but date of enlistment is listed as April 23, 1943.
Verify all of this independently. Databases can have errors, I could have made mistakes transposing, etc.
P.S. Incidentally, are you aware that he has been entered in the National WWII Memorial registry by his niece, Linda J. Hallahan? The listing has the same info you have cited, so I'm guessing you are already acquainted with Ms. Hallahan.