Since this thread is back, I might just answer one question left over from four years ago. The mysterious covin in the MacColl collation (verse 6) is really calving. He seems to have have taken that verse from Bell Robertson's text (Greig-Duncan Folk Song Collection, II, 74); the final word of the verse would then be enow, not anew. The confusion there may have arisen from MacColl's altering the pronounciation of the word to make it fit better with his idea that Bell's "plough" ought to be pronounced "pleugh".

MacColl's natural accent was not Scottish, and he sometimes over-compensated a little when performing Scottish material, making it difficult to be quite sure what he was singing. This can also lead transcribers to try to represent his pronounciation instead of the word he was actually using; Bell Robertson, for example, wrote down most of her song texts herself, and her spelling is often a useful guide to the way she herself would pronounce the text (she didn't sing); thus, she appears to rhyme "coos" and "ewes" where MacColl has instead gone for "cows" and "yowes".

Verses 4-17 (see Stewie's final transcription above) are from Bell's text (perhaps also verse 3). MacColl has made changes of details, of course, and omitted some text, beside changing Bell's Sweet Willie to Lord Thomas throughout. Interestingly, the word really was "hat" rather than "heart"; there is a preceding half-verse, omitted by MacColl, which would have explained it:

Willie put his hat on Annie's head
In the middle o' the kirk.