From what I can tell, ac-pb.it seems to be too big to be used with JJ2, even as a j2b file. I'm not particular fond of that mod file in any case. Some mod files just can't be used in JJ2 levels because of their size, although sometimes the problem may lie in part with the contents of the level. Most music files over 2MB don't work. It's a whole complicated mess that I don't want to get into right now.