I have a little data on DONALDSONS of Loughans and will be glad to share. Have you researched parish registers, the Tithe Applotment books, or Griffith's Valuation? There is a lot on the DONALDSONS there. Also, at PRONI in Belfast recently I met a DONALDSON researcher and can give you his contact information.
My interest in this family comes from HADDEN research in southern County Tyrone: an Archibald HADDEN of Loughans and Doolargy (one of several related men of that name) married Margaret DONALDSON before 1844 and baptised children at Ballygawley Presbyterian Church. Many of the children in the area (including Haddens) attended Loughans school, which was operated under the Presbyterian church. The old stone school house is still standing, but it's in derelict condition.
I don't have my complete files here right now, but Archibald HADDEN would have been born about 1810-1820 and died in the 1880s. His estate administration is listed in the WILLS INDEX at PRONI, although the original will was destroyed with thousands of other records in the 1922 Four Courts fire in Dublin.
Archibald HADDEN's wife Margaret DONALDSON died after the 1901 census, see below.