I search the IFHF's online database at ROOTSIRELAND.IE. It has abt 20 M church/civil/census B/M/D records for MOST Irish counties. Records before 1863 are increasingly sparse and almost non-existant before 1800. Protestant records are the LEAST likely to have survived.
I looked for a ? Linehan and ? Nowlan marriage in 1870 +/- 6 yrs, in all Ireland, with the parents' names unknown. I found 0 records. Either they married elsewhere, the records haven't survived, or the records haven't been transcribed. Parts of Co. and Cork City records await transcription. Suggest you visit the database, register (free), and opt to be notified as records are added (also free).