I found a few excerpts from Lawrence Booth's Book of Visions by Maurice Manning to help you see how the voice is similar for both boys. Both are considered "hillbilly" in the most ironic sense as they are both wise beyond the adults of the narrative and both speak in ways that are meant to seem them more self-taught than traditionally educated. Again, class informs the dialogue here more than race. And I am still interested in how you see the Berryman tendencies playing through some of the idea behind these poems.
Anyway, this little excerpt shows you a line or two in Law's voice.