Used all the resources I know on the internet and nothing definitive. There is a Jack Callahan of Pasadena that participated as an equestrian rider in the Rose Parade 1961 to 1977. Yearly newspaper articles listing parade participants. CA Voter Registration has one entry for 1954 of a Jack E. Callahan 10433 Kingerman Street (D) Precinct 61 Los Angeles County CA. Today maps has this address in South El Monte, CA.
http://www.vitalsearch-ca.com/http://www.vitalsearch-ca.com/has CA Death Index for 1940 to 2000. A few years ago it used to be free but now requires a subscription. I would find people on this index that were not in the Rootsweb/Ancestry CA Death Index 1940 to 1997, for all years.
The SSDI really is not that comprehensive before 1960 and before about 1986 only those that were receiving SSA benefits at the time of death are listed, as children didn't require a SSN till they started working abt age 16. In other words if a person with a SSN died before they were receiving benefits before 1986 they would not be in the SSDI. So if Jack died before abt 1983 (if he wasn't getting any SSA benefits) he may not be in the SSDI. I don't know what year it stared but all funeral homes are required to report the names of the deaths they handle to SSA, so today all persons who die are listed regardless of age.
Try Find A Grave or Internment.net in the future.
The SSA has a program will deliver a letter to someone for you. You write the letter then put it in an stamped, unsealed envelope with just the name and take ot to local SSA office.The SSA will read it to make sure it is non threatening and address it to the last address they have and mail it. Try will not tell you address nor will they know if it was received, if it gets to the person they may or may not contact you back. Now I don't know if you need the SSN already, check with them.