As others have stated, there are no rear subs on the base model. The holes are still there so that aftermarket speakers could be placed in the same location. I have attached a photo of the inside of a Crossfire that shows where the speakers are. In fact once you see the location, you can find the speaker holes in your car buy pressing firmly on the carpet that covers the bulkhead. There is nothing covering the speaker holes but the carpet. I plan on upgrading the stereo myself once I sell my '73 Cougar.

I believe that the speaker size is 6 1/4 or 6 1/2. Check with Crutchfield to get exact specs whether you buy from them or not. They are a great resource.