Nowadays plugs are put in with anti-sieze and teflon tape. And lots of torque, so it takes a lot of torque to back them out, which means you need a really good grip on the barrel, but not so much that you will dent or mar the barrel. Shift all that to an old set of barrels and some possible rust on the threads, and you could have a real job on your hands.
That said, how important is it that they come out? I'd sit back and think about it, listen to some of the others here, and see if someone can offer up a professional that is familiar with the task.
Success!
