There shouldn't be any need to rig up anything or solder, as they feature slide-on connections.
Madisound is probably the leading source of Dunlavy replacement drivers and my guess is that what they are telling you is correct. Dunlavy used cheap, easily replacable tweeters. As I mentioned above, you just have to fight a little bit with the felt surrounding the tweeter bay when you install them. Be certain to give the new tweeter 100 hours to break in before drawing any conclusions (it will need 200+ to fully come around). I also don't recall whether wrote that you need one or two, but you should replace the pair to ensure proper pair matching (this is important).
My Dunlavy dealer sold a lot of used Dunlavys, and he would generally replace the tweeters before reselling just to avoid problems, as in the Dunlavy implementation (first-order crossover and cheap driver), they tend to burn out.