This is a fascinating surname. A search with Google reveals:
“The surname McClughan is of Scottish and Irish origin, frequently associated with the Hebrides, the west coast of Scotland, and Ulster. It is believed to be derived from the Gaelic MacGille Eathain ("son of the servant of Saint John") or MacLuachain ("son of Luachan"), meaning "son of the swift/nimble one".
According to PRONI’s Guide to Church Records,
https://www.nidirect.gov.uk/publications/guide-church-records, the following Protestant church registers, with commencement dates, survive for Dromore Parish, County Down:
Dromore Church of Ireland, baptism registers from 1784
Dromore Methodist, baptism registers from 1827
1st Dromore Presbyterian, baptism registers from 1832
Dromore, Banbridge Road Presbyterian, baptism registers from 1851
Drumlough Presbyterian, baptism registers from 1827
Microfilm copy of all these registers can be examined in the Public Record Office of Northern Ireland (PRONI) in Belfast.
In addition, the early-19th century Tithe Books for Northern Ireland, which are in effect a census of rural heads of households, can be viewed online, free of charge, by searching PRONI's e-catalogue at
https://www.nidirect.gov.uk/services/search-pronis-ecatalogue; select ‘Browse’ button and enter FIN/5/A/113 in the search box and this will return the tithe book, compiled 1834, for Dromore Parish, County Down. By selecting the appropriate ‘View’ in ‘Digital Record’ column you will be able to view a list of all landholders, by townland, in Dromore parish in 1834. Hopefully you will find some McClugans.