Mystery Monday: Grandfather Where Art Thou?

This is part of the Mystery Monday Series.

Today`s post is about my husbands elusive maternal grandfather.  I am posting this information in hopes that somebody out there knows something and can contact us regarding a lead on this.
His mother was born 22 Feb 1941 in Pana, Christian, Illinois. Her birth mothers name was Claire Lucille ALLEN. She was adopted and raised by her Maternal Grandparents: Granderson "Jack" ALLEN and Alma Ruby DAPPER.
We would like to find his Biological maternal grandfathers family. Just to be able to know who he was and to learn something about him, to be able to fill in that section of his family tree for our children and our grandchildren.
It is highly possible that my husband has multiple DNA matches that are from his line but we have no clue what it is to even look for without any more information.
If anyone knows anything about possibly having a daughter born in Christian County, Illinois we hope that you would come forward.
His Grandmother was living in Saint Louis, Missouri in 1940.  The family was living at 5369 Arsenal Street in Saint Louis City, Missouri.  Claire was 19 years old.  Claire was working a housekeeper for a private family. No other information about her occupation was given. Could she have met my husbands grandfather as a result of her occupation? Her parents Granderson and Alma were both working as Hospital Attendants, it specifically stated that Alma was working for the City Hospital.
Claire served in the Navy, in the Waves in World War II. The family previously lived in Montgomery County, Illinois. They may also have ties to the Chicago area. They were a devout Catholic family and each of his grandmothers siblings as well as his mother attended Catholic  School. Claire had three siblings: Gerald, Jerry and Jean Evelyn ALLEN. Pictured in the photo above is my husbands mother and her Uncle Joe ALLEN.
I do have a lead that I am working on right now. I am reluctant to share any more about it at this time.  If anything pans out with it, I will share but for the time being I have decided to keep it under wraps. It could be something but then again it may be nothing at all, just a hunch Ive got. Stay tuned and if you know anything, by all means leave us a comment below!