I'm only familiar with Michael Cooney's rendition of Charley Butler's version, and, without finding the vinyl and playing it, I'd say the missing line is
Diamond Joe, where you been to?

Cooney learned it from the library of Congress recording, and he tells about a buddy in the background egging the singer on and telling him "gwan, you can do it", and also providing some backup.
Art? Does that sound right?
And Art, I do recognize your added verse as coming from that same Cooney album, only it belongs to Leadbelly's "Corrina". I got that album just after Malvina Reynolds died, and I used to sing "Thyme, It is a Precious Thing" as a way of grieving for her. The album and that time meld in my mind. 1977?
Blessings,
Barbara

PS Art, I drove through Depot Bay July 3 for the fireworks there, and thought of you. It's all cleaned up and touristified, and I don't think you'd like it if you recognized it, which you might not. Sorry.