My comment on the hand/horn question was based not on listening to MacColl's singing, but on MacColl's own transcription of the words: his understanding then, rather than mine.

As for 'spey', Alexander Warrack's Scots Dialect Dictionary (also issued as Chambers' Scots Dictionary) has 'spey same as spae' and 'spae n the opening or slit in a gown, petticoat, etc.'