I found some information that is likely his. Very little of use or for sure yet. I might be able to add that he was born in April, 1955. He, like many people, used more than one name and variations of his name. I might have found him though. I have a possible sister of Mark Cagle born in 1953. She and her family including her husband and her father have quite a bit on them. His findagrave site and his obituary both mention son Mark but not middle name. There are many Marks and several with A as the middle initial, but none that I have found can be attributed to the one described above. There is the possibility that it is your father.
I found this family already put into wikitree semi-issolated and without profile managers. It describes the same people I described above:
Here is findagrave on the possible father of Mark and family:
Because the people we are researching are alive or even possibly alive, privacy issues make them tricky for tracking. Maybe you can find out who originally entered these profiles and ask them for Mark's middle innital, date of birth, or anything else they are willing to share. Telling them who you are and what you are actually asking for is the best way to prompt a response.
I'll let you know when I know more. Good luck hunting!