The major source for researching ORRS in the County Down is Ray A. Jones "Ulster Pedigrees. Descendants, in Many Lines, of James Orr and Janet McClement, Who Emigrated from Scotland to Northern Ireland ca. 1607". The title says it all! Jones's book is based on the ORR family-trees drawn up in the 1830s by Gawn Orr of Castlereagh (they were mainly based on headstone inscriptions) and deposited in the Linen Hall library in Belfast. I wrote an article about my own researches which was published in 1988 in FAMILIA, and I counted no fewer than 501 separate surnames in the index to the above book, making it a priceless resource for Co. Down genealogy, especially as many of the headstones read by Gawn Orr have since disappeared. All the names mentioned in postings on this thread, e.g. McCune, McCormick, Frame, are in there somewhere.
Harry