Spica used mids with rubber surrounds so I am assuming it is a tweeter.
Your problem is that Spica crossovers are critically matched to each driver. So the speakers/crossover are matched together. Popping in a replacement driver isn't going to necessarily restore this wonderful speaker to the point where you will be able to appreciate what they can do.
You might want to talk to Danny Ritchie from G&R Research (has his own forum here on audiocircle) who might be able to give you some good advice. Treat these speakers like the landmark design that they were and you will not be disappointed. What I mean by that is they need to be restored, not modified or "hopped up".
