You're three quarters the way home. You've correctly identified the two airlines involved as well as the CRJ between BFS and BHX. However, we're looking for an aircraft just a wee bit shorter than the A330-300 out of SNN (Hint: It's not the -200 variant)
I'm not really one for the mechanical detail of aircraft. However, was this when Aer Lingus were leasing in a World Airways MD-11 for several summer seasons ? Was that doing the same run most days, New York-Shannon-Belfast ? And is that a bit shorter (though wider) than an A330 ?