Henry VIII decreed that all his churches (he allowed only one) keep B/M/D rcds. This included the Church of Ireland. However, the earliest surviving parish registers in the Irish Family History Foundation's database date to about 1680 - These are few and far between.
The English church (or at least its parishoners) began splintering into additional Protestant sects in the early 17th century: Presbyterians of several stripes, Puritans, Methodists, Baptists, Quakers, etc. These were all considered "dissenting" churches. The edict to keep rcds wasn't interpreted in practice to apply to them; Therefore, they didn't. Consequencely, rcds for these sects are sparse, sporadic, and poorly rcd'd for the largely Protestant Ulster Province (Antrim, Armagh, Down, Derry, Tyrone, and Fermanagh). Your McClanahans were likely Scots-Irish and hence Presbyterians.
Before you visit Ireland, you should contact the Public Records Office for Northern Ireland (google PRONI), and the Ulster Historical Foundation. I believe both are sited in Belfast. For the latter, its B/M/D rcds are already in the IFHF database. However, other documents which can't be easily digitized are in the UHF's offices. Even though Ireland is split, their genealogical, historical, and archival organizations cooperate (even if grudgingly). There is a slight chance that info on your family could be found in the National Archives of Ireland, or the National Library of Ireland. I believe these are both in Dublin, but have websites.
For the McClanahan forename, just visit the IFHF database by googling "Irish Family History Foundation." Register and browse for free. Only if you get serious and want details is there a fee.