Very good work, indeed, Gibb!

Something else of interest. In North Carolina in 1922 or 1923, Frank C. Brown collected a call-and-response work song called "Sheep Shell Corn by the Rattle of His Horn." that scans like "Blow, Boys, Blow," and bears a tune that shows some slight resemblance:

http://www.archive.org/stream/frankcbrowncolle05fran#page/134/mode/2up

The chorus, "Blow, horn, blow!" at least makes more obvious sense than the shanty chorus. That suggests to me that it might be the original, but the evidence is too slim to allow a conclusion.