The C6 is the same as the Am7, and it can be used by itself with many chant-like Southern convict work songs in Am that fit the same basic pattern as Goin' Back to Weldon. That's because the Am7/C6 is almost two chords rolled into one. There's an full Am in there (a + c + e), and there is two-thirds of an Em in there as well (e + g).