Debra,
There is nothing for either Mungo or Sowell in the book. There are however entries for slaves with the first name of MINGO, in Chowan and Franklin.
In Chowan County it refers to two slaves by the names of MINGO & DOLLY who petitioned in 1808. There is no mention of what surname they may have been given.

Another MINGO is mentioned in records from 1777 regarding emancipated blacks that had been "taken up and sold by order of the county courts of Pasquotank,Perquimons, and Chowan". This MINGO was property of CALEB WHITE.
In Franklin County, there was MINGO GREEN, who was freed by his owner, CAPT. WILLIAM GREEN, in 1822. This MINGO was a preacher.

If you think one of these may be yours, let me know and I will post the info.

Deloris