Hi,
I made a spacer ring and retaining bracket to allow fitment of 6.5" Pioneer Components in my Sapphire. Apart from four screw holes, no cutting of the door cards was required. This sounds way better than the standard 5" components (that had perished).
The rears are 5" but I have seen plenty of examples of 6" and 6x9's fitted to the rear deck. Again a spacer is required.