Caveat: I know some old songs, but I don't know anything about their history. I think "Man of Constant Sorrow" is derived from what people call "East Virginia."(We sing "old Virginia") Barnett said to Wolfe that he didn't think he wrote the song, and I believe him. Here are the lyrics I know.
I was borned in old Virginia
To North Caroliner I did go
There I met a pretty girl
But her name I did not know.

Her hair was of a darksome color
Her lips her of a cherry red
Her breasts were of a snowwhite color
Where many a night I lay my head.

I'd rather be on top Black Mountain
Where I know the sun refuse to shine
Than see you be another man's darling
And know that you would not be mine.

I am a man of constant sorrow (Pronounced more like "sorrer")
And I seen trouble all my days
I'm going back to old Virginy
The place where I was partly raised
Learned in 1966 or 1967 in Durham NC from Forest Covington
The tune is somewhat similar to the "O brother" rendering but it is simpler, much slower and softer. I think of it as a lament, not a bluegrass song.