I originally bought 6x9 to 6.5 adapters from crutchfeld for the front. They fit the OEM front speaker mounts, but not my 6.5 speakers. So I made MDF adapters, which, IMHO are better anyway in terms of resisting vibration & rattling. The rear 6.5 speakers use an integral plastic (at least in my CC w/RF) mount that bolts to the door. So I think you are going to need to make adapters for the rear also. Here is how I made them for the rear:
Changing Rear Door Speakrs in CC w/ RF
The first post includes photos showing the OEM rear speakers.