I have original Hartsfields with the 075. You don’t get a lot of sparkle but you do get the extension.
Not knowing how accessible the tweeters are assuming they are in ring clamps. Have you ever thought about dropping in a pair of 2405's/077's? The alnico's all use the same body no issues fitting them in. Overall a better tweeter much better dispersion and more extended to a little over 20K. Might add some of that missing sparkle. I have a pair in my 4344 clones and they do sound good.
Rob
