This is a typical and nearly fruitless endeavor. Take a classic, iconic unit and improve it without changing it or ruining its marketability. These old units are what they are. Improving them requires changing them. Changing them makes them something other than what they are.
I don't mind if an owner does whatever he/she wants with old speakers. Just realize that once someone starts mucking around, they're not the same speaker, and if you don't want the same speaker, then why get it in the first place?
So you can improve it but not change it? Seems like a contradiction to me.