Searching for Fathers Birth Sibling born in Michigan 1968-1970

Hello. Recently my grandmother told my father and I that she had to place a child up for adoption in Michigan around 1968. My grandmother is experiencing early stages of memory loss so we are unsure of exact dates and question the sex of the baby. She firmly believes it was a boy. She lived in Kentucky and had to move to Michigan with her aunt and uncle during the pregnancy. In 1968 they lived across from the Cadillac plant in Detroit so we believe that the adoption may have taken place in Wayne county but again are not 100% sure. We have searched for hospitals around the old Cadillac plant in 1968 and think that the place of birth may have been the Henry Ford Hospital but this is just a guess at this point. My grandmothers name is Mary Lee and we are not sure if any information was given to the child. My father would love to learn more about them as he would have been around 2 when the birth occurred and they would be his only sibling. My grandmother (the birth mother) would have been in her late 20’s at the time of adoption. She is white and the birth father was also white. We are not sure of what date exactly the child would have been born. We would love to make contact with them. The adoption we are told, after searching the Central Adoption Agency, that the child was never a ward of the state so the adoption must have gone through an agency. We are willing to search any possible lead.