Could Isom/Isham Adkins Slone's father be Isom/Isham Adkins, a son of Parker Adkins?
Isom/Isham Adkins was born in 1757 in Halifax County, VA, and is reported to have moved to Kentucky at some point. No other information is available, to my limited knowledge.
I mention this possibility only because I have read elsewhere the supposition that Isom/Isham Adkins Slone's father was reputedly Parker Adkins, 1720-1792. Unfortunately, Parker Adkins, who was long married to Mary "Polly" Littleberry, would have been in his 70s if this was true. However, what if Mary Alice Sizemore had a liaison/marriage to Adkins's son Isom/Isham, about whom no further documentation is apparently known other than his birthdate. It seems worth pursuing, given her son's given name.