Propane and nails are kind of crude for the Irish. Those cats knew how to make bombs..
I agree.
This isn't your father's IRA. They don't have the men, materiel, funding they used to. They don't have the Eastern Bloc or the Libyans to send them C4 and provide training any more.
If a IRA splinter group tried to pull off a big caper, it'd look a lot like an Al Qaeda attack. Or a Mafia bomb. Or a couple of clever and ambitious kids a la Columbine. Without more solid information, it's just a guess.