According to the Social Security Death Index the Richard A. Gatter who died on September 29, 2009 was born June 3, 1929. The birth date does not match exactly as Lee posted at the link I posted before. However, there is still a good chance they are the same person. There are too many coincidences to ignore the possibility.
The best way to trace back would be to have your grandfather's death certificate or obituary to confirm who his parents were and see if they match the Harry and Natalie posted by Lee.