Hi John, I also posted this to your query on oldtimey newsgroup - it may be what you are looking for. The last stanza of the version on Dirk Powell's 'If I Go Ten Thousand Miles' (Rounder CD 0384) is unusual. Powell noted that he learned the version from his grandfather who had claimed 'these events took place right up around Greenup, KY'. Dirk says that, not being an historian, he 'wouldn't speculate on such things'. The vocal is solo - by Tim O'Brien:

William he travelled to far distant lands (x2)
And the farther he travelled the faster he ran
All that he saw was the face of his love (x2)
And all that he heard was the cry of the dove

--Stewie.