My wife's family (BLACK) has a member that married a Peter S. Whisenant within an appropriate time-frame to be the Peter Whisenant you are seeking.I don't have any back-story on Peter, but plenty on the Black and Cash clan of Georgia and Alabama.
Genealogy Info Below:
Malinda BLACK. She married Peter S. WHISENANT 23 NOV 1856 in Habersham Co., GA.
Malinda's Parent info...
George Washington BLACK Sr (Thomas BLACK Sr1) was born 1790 in SC, and died 1842 in Habersham Co., GA. He married Mary "Melissa" GOSS 1817, daughter of Thomas GOSS Jr and Elizabeth PUTNAM. She was born 1801 in Pendleton Dist., SC.