My name is Zelda. I have Clarke, Suggsville, Alabama connections. I I just read your post this morning and looking at the date you may have answers regarding your Margaret Portis. It's my belief that it more likely than not that Portis was the surname of the slave owner. My 2x great grandmother Margaret Johnson is also on the 1870 census and lived in close proximity of your Margaret.
In my research I met a great niece of John Wesley. She is a wealth of knowledge of the Portis family. John Wesley also had brothers who were in the surrounding counties including Sumter. She also has papers and pictures. In a discussion we had it was her belief that the children of Johanna Portis on the 1870 census were direct Portis descendants with John Wesley possibly their birth father.
If you are interested in contacting this person please email me firstname.lastname@example.org