I would really like to see some pics on a replacement tweeter install.
But anyways... I have a set of Alpine SPX-1772 2-way component speaker I will eventually be putting in my car.
In my Integra I initially had a shop install all of my aduio equipment which I ended up regretting because instead of using/making new speaker rings for the front door speakers they cut the backside off of the OEM speaker brackets and used them the same way a lot for you guys are. It works and in most cases gets the job done. But in my Integras case one of the speakers broke loose over time and ruined a top of line set of speakers. But that was mostly because of the shop who installed them, it could have been done much better.
the other major reason why it didn't work was because the bolt pattern for my alpine mids was larger in diameter than the bolt pattern for the OEM acura mids and there was barely enough material to bolt the speakers to the spacers
The OEM Si speaker mounts seem to have much more material to them than my Integra mounts did, but either way I still think the right way to do it would be to use MDF speaker rings or make your own.
Here are what mine looked like in my GSR and will look like in my Si.