Speed the Plough has a long history in Scottish manuscripts - the Dashing White Sergeant started out I believe in England. These sort of tunes are so old and with coloured histories that any claim to sole origin authenticity is not going to stand up.

Without responding to anyone in particular. 'Your' source of 'your' music is important (style and content) but it's rather more complex than 'written down by someone who lived in the same geographical region as me 300 years ago'.

Think carefully about the ending in Miss Macleod of Raasay - it doesn't actually finish.. can be done, but tricky.