I am not related to this family but have many family branches that come from this area.. as such i have numerous records on my machine and with the detailed information you provided i was able to find a number of records quickly..
Here is the ireland marriage record for the McAlister/O'hara marriage. It will provide their native townland which is not transcribed on the LDS listing.
Some baptism records..will help you with an exact birth date and lists godparents which could provide some leads.
From doing research i know that every additional piece of information helps... Good luck in your searching..