I'd GUESS that the Wilbur H. Japs listed in the Social Security Death index is the son of Frank A. since the name is a touch unusual and has the same middle initial and year of birth. Wilbur died 6 December 1996 in Louisville, Jefferson, Kentucky. You would need to prove it by either getting the death certificate from Kentucky or requesting his social security card application. That Wilbur's social security card was obtained in New Jersey.
Again, this is not my family. This is just information pieced together through census and can have errors. It is my "best guess". Looking for this information has made me realize how uncommon the Japs surname is. I need to talk to an elderly Japs "cousin" and see if this is familiar.