As I have no better explanation to offer I could live with that one. Any mention of a 'tower' is certainly out - I've compared the transcription Jon Bartlett thankfully provided to what Ewan sings on 'Black and White - the Definitive Collection'. Also, I can't hear any mention of 'sib', only 'sin'. As he sings the last line a lot quieter than the rest it could well be 'sinned', although neither makes grammatical sense.

The narrative lines seem to be fairly straightforward. I'd suggest two changes in verse 8, though: Ewan sings 'yin', not 'ane' at the end of the first line, and 'Ere' (before), not 'E'er' (ever) at the start of the second.

Gordeanna McCulloch sings a version with the 'And we'll never go down to the broom any more' refrain, but I haven't worked it out fully.