Hello Anne.
Still having no luck with Dennis I'm afraid - did he have any other names that you are aware of

There is a WW2 Draft for Francis McKeown with a birth date of 11 Feb 1894 Belfast. Wife Margaret.

If this happened to be the correct one then there is also a
SSDI Record Francis McKeown
Born: 11 Feb 1894
Died: Dec 1982
Last Residence: 07961 Morristown, Morris, New Jersey.
SSN issued: Railroad Board (Issued Through) (Before 1951)