The old ones I believe were mounted with a clip that was threaded to the tweeter itself like these:
These mb quarts can be held in by a screw in the rear; if you look at the pic of the completed inside panel in my 2nd post, you'll see a shiny dot on the tweeter, that's the thread. They came with brackets that may or may not work, not sure, but the bracket is pictured in the 4th pic on the left.
As for sound, IMO it sounds great and the front stage is completely improved. I'm running a Clarion Pro Audio DRX9275L, USAcoustics USX4065 4-ch pushing MB Quart RKB 130s in the kicks, and now the OEM mids & MB Quart 19.02NXs which are actually identical to the tweeters on the kickpanel speakers. The gain is quite a bit lower on the mids/tweets, so theres a nice balance between the 6 speakers up front.
MB Quarts are pretty much the only speakers I will buy, they sound incredible compared to most and were well worth the price of $65US shipped.