Hi RonSSS,
Interesting.Actually as i said before a lot of people have tried to change or add tweeters to their 420 and the suggestions vary a lot both in terms tweeter's location, type(compression,dome,ribbon...) and crossover frequency.I have so many problems with the cross over of my 604 D that i hesitate getting involved in a new crossover adventure!That why i try to get specifics about optimal crossover design and components for a selected tweeter before pursuing.
Charly1944.