The point of giving you a link to a page with guides about doing Slavery Research was to show you where those kinds of records can be found and how to use them.
The Cohabitation Marriage Records I mentioned were from the book "Somebody Knows My Name, Marriages of Freed People of North Carolina" by Barnetta M. White. The original records are on microfilm, too, a few of which some of the NCGenWeb County sites have transcribed for some of the Counties, although not for Nash or Halifax.
As for FamilySearch, they have Probate Records and Estate Records, which are where you will find wills and estate records with slavery inventories. But as I said, you first need to do some research on the families nearby those where yours were living in 1870 to try to pinpoint which one of the families yours may have come from. Slave research is not easy, and it takes a lot of time, but it can be done.
I strongly suggest that you look at some of the websites I mentioned on the African American Research page I gave you, so that you will have an idea of what and how to do the research.