McLain/McClain Families around Shankill, Co. Antrim

[ten7d5]

Hi everyone, I've been doing my genealogy for 5 yrs but have no experience with irish records since my entire family's been here in NY since the early to mid-1800s.
Anyway, my paternal great-great-great grandfather was Henry McLain born in 1831. I am suspecting Antrim because it had the most of McLain surnames with that spelling.
As far as the family goes, I know that Henry had a brother John that emigrated to NY around 1851-52 and opened up a painting business in Yonkers, NY. Henry followed with his wife Anna in 1865 and she gave birth to my great-great grandfather there in June 1866, two daughters came soon after. Henry McLain died around 1872 and his son Henry's last name was changed to "Beal" after Anna remarried in 1875. I only just uncovered this about a year ago, its' been a big family mystery.
I sent a search request to Eneclann to see if they could help me but since I cant find Henry McLain's death certificate I have no idea of his parents names or exact origin in Ireland.

If anyone can give me some guidance as to what records to go to or if I should look in a different area of Ireland, it would be well appreciated. I'm also looking for access to the 1851 ireland census for the entire island if anyone knows where to get it on CD-rom, etc.

Thank you very much,
Christopher Beal