I recently used a web site to locate some long lost family. The web site is www.zabasearch.com
. I did a search for a William Neal, and there is a William L Neal listed in East Alton, IL. This William was born July 1946, which is a little older that your estimated age. The phone numbers are 618-258-8677 and 618-258-8687.
Good luck on the search for your father.