A couple more pubs in Castlewellen....
The Old Tom
On the square, in town.
Kind of an "old man" pub, but enjoyable people and conversations.
The Fountain
Just as you're coming into town.
Nice, historic building.
Maginns
On the lower end of town
Maginns Bar Castlewellan
A good one in Newcastle is Quinn's - and they have good food, too.
Quinns Website
Down in Newry, the Quayside Inn had good food.
(These are all places that I have been to, but it was about 13 years ago)