A.A. Collins Funeral Home records, Pemberton, NJ. courtesy Mrs. Elma Eckert, Mt. Holly , NJ 1996
wife's death information lists her as his widow on Dec 20, 1948.
I happened to have collected this isolated Nixon "fact" when working through some records donated by Ms.Eckert to the Gloucester County Historical Society. The Funeral home, if it still exists, or if another is operating in the same location, might have a record for where they are both buried and when he died.
Location of graves is not always where you might think. Perhaps not where they lived but where other family may have already had plots so convenient when needed in a hurry. Just a suggestion. Another possibility would be contacting Veterans organizations or officer at the County Courthouse, who should keep a record.
Good luck with your search.
Valerie Nixon Caulfield
Salem county, NJ