Or, you might get a recording & listen to the chords. I used to have a record, one of the ones where someone from a college went to get him from the prison & record him playing & sold it "for posterior" which was a wonderful piece of history, I thought. He played open chords, used no capo, and tuned a guitar to not exactly concert pitch. Nevertheless, one may listen to the songs he played & sang, & hear the exact chords he used. Your local library might have a recording, otherwise it might be hard to find.