This is gonna be an unpopular option...
I cut my kick panels (in 1997) and mounted speakers directly to the kick panel itself. My original speakers (Rockford Fosgate Fanatic P's" were 'just' a little too deep for the space so I ran 1" spacer rings.
During my restoration I kept the speaker holes since they were already there but this time I sealed the two separate spaces inside the kick panel from each other. Inside there's one cavity connected to the cowl and another cavity connected to the A-pillar/door pilar and rocker panel.
These 6.5" Kicker components fit without the spacer rings, there was enough space behind the speakers for some acoustic foam too.
You must be registered for see images attach
You can kinda see the patch I glued in if you zoom in on this picture, you can also see where the factory door pilar was.
You must be registered for see images attach