I can hear both 'Old Black Joe' and 'Bonnie George Campbell' in Cohen's melody (?)
Stephen Foster, who wrote OBJ, was heavily influenced by Scottish folk music melodies and George Pullen Jackson, writing in the Musical Quarterly about Foster's debt to folk music, points to the similarity of OBJ with Saw Ye My Father AKA the Grey Cock. The melody was also used for the religious Shape Note Hymn 'Saw You My Saviour'. The article is very instructive but far too long to transcribe here. It's in the Musical Quarterly, Vol. XXII, 1936.