HD, if you ask your question on the Madisound forums, I'm sure you'll get an answer. Several years ago, they helped me fix up a pair of Polk SDA-1 speakers from the 80s that had a blown tweeter and a blown mid. I've hung out there ever since. There are some people there who are sharp.
I'm not talking about sharp because they have a stereo and they think it sounds good... there are a couple of guys there who I'm sure will know the full tested specs of the original drivers and be able to offer a good choice for a substitute with suitable specifications.
http://www.madisound.com/cgi-bin/discuss.cgi