This sounds very intriguing.
Can you provide a time frame, and whatever evidence leads you to believe that Gerald CLAY used the name Harry GIBBS at some time?
It appears that Gerald CLAY is listed accurately in the Social Security Death Index.
I did find this interesting newspaper item:
Friday, May 18, 1917 Jackson Citizen Patriot (Jackson, MI)
The police and sheriff’s departments have been asked to aid in locating Gerald Clay, the 13-year-old son of Mr. and Mrs. Archie Clay, 131 Ten Eyck street, who has been missing since a week ago today. The boy attended the Pleasant street school. He started toward school as usual last Friday morning and has not since been seen. He became involved in trouble with some other older boys about ten days ago and it is believed he took fright and left home. He wore a brown suit, brown cap, blue sweater and black shoes. His hair is brown, eyes blue, light complexion. He is about 3 1-2 feet in height and weighs about 80 pounds.