Those are resonators, the mufflers are at the back. If you want it QUIET, like stock (inside the car) get a Flowmaster Force II cat-back. If you remove the resonators, you just get drone inside the car. If you don't mind a little more interior sound then get the Flowmaster American Thunder system. The great thing with the cat-backs is that you can install them yourselves and save labor cost.
Remove the mid mufflers and put in dynomax 24250's. Sounds great on a scat pack. Any good muffler shop will make any inlet/outlet work as long as it is larger than the current diameter. These are 3" in and 3" out. I don't know the size of the exhaust on the R/T but the scat pack is 2.75".