Hi John,
I know the following does not answer your question, but I thought you might see some connection.
I also have the name Crombie from Co. Down. My main line is from Elizabeth Crombie who married Thomas Carson in Rathfriland in January1873. She was the daughter of James Crombie and Margaret McCulloch and her marriage details state she was born in Lackan in about 1852.
They had moved to Irvine, Ayrshire by December 1873, and father James joined them some time before his death in 1884. His parents were James Crombie and Sarah McCreadie.
My Elizabeth had a brother Thomas b. about 1846, who also had come to Ayrshire before 1879, with his wife Mary Jane Gibson. They had 8 children, some born in Ireland and some at Irvine, Ayr. There appear to be a large number of Crombies descended from this couple's children.
One of the sons, Samuel married twice, the second time to an Elizabeth Crombie, also from Ireland, and her parents were John Crombie and Ruth Martin or Priestly (differs in documents). They lived in Renfrewshire near one of Samuel's sisters who had married a John Dalzell. I have not researched her parents as yet.
There was also John Crombie from Irvine, originally from Ireland, who died in tragic circumstances (a workplace fight) in about 1886, but I have not yet proven a link to him.
Anyway, if you see any connections, let me know...I am happy to share what I have.
Nina