You'd be thinking of Ray Fisher's The Bonnie Birdie, I expect; it isn't really a "version" of Musgrave, though the basic plots are quite similar. Although the Christy Moore recording of Musgrave has its admirers, he learned it from a Nic Jones record (although Christy seems later to have claimed to have written a few verses himself, I'd put his contribution at more like two or three words) and for myself I'd rate the Jones set rather higher.

Disregarding individual arrangements, there are far too many fine songs in the ballad category for me to play favourites. I'll just be difficult, and confine myself instead to disqualifying a few suggestions already made.

There isn't any evidence that Palace Grand is even as old as the Civil War, though it may be, a little. It's always struck me as a typical parlour ballad of the later 19th century.

The Great Silkie is certainly old enough, but was a purely local ballad and has never been found in tradition outside Orkney and Shetland.

Greensleeves, so far as can be told, is an art song; though forms of the melody have been found in tradition -attached to other songs, or as a tune for the Morris dance- and the tune may be older than the words.

The Gathering of the Clans (The Ball of Kirrimuir) is certainly older than the American Civil War, but wouldn't generally be considered a ballad.