The dimensions of the openings are on this link:
Info - Pics of inside door panel with speakers - Civinfo Wiki
You can measure your own speakers to make the support rings. I made some out of 19mm MDF, see this link:
Rear Speakers - Replacement with Coaxials (3 Door)
I used the self tapping screws / clips that came with the infinity speakers. Holes were pre drilled in the door panel first + a bit of waxoyl to stop corrosion.
Hope this helps.