A gaff is a house
Rachman was a notorious landlord who ripped off all his tenants with ridiculous rents and lousy houses
Abune is Scots for above
i suggest that if you're into traditional scottish songs you obtain a copy of Chambers Sots dictionary. For contemporary Glaswegian see either "the Patter" published by Glasgow City Libraries ot The hilarious "Parliamo Glasgow" by Stanley Baxter