Your stock exhaust has a ball and socket connection on the outlet of the resonator (sometimes called the "suitcase). The tip in your picture has a straight connection, which means it will not simply bolt-up to your car. It will take some welding and/or cutting to attach that.
Here is a picture of the factory exhaust tipsخ. See how short they are and the bell shaped connection. That's the length and type of connection you need.
Pipe size for an automatic R/T is 2.25" and for the 6 speeds it's 2.5".A good muffler shop can cut the exhaust back and then the tips you posted would work. You couldn't just mount those tips cuz they probably would stick out too far so you'll more then likely have to cut the tail pipes anyways.
I'm not sure what the pipe size is for an R/T but I'm sure someone on here knows.... then get those tips for the correct size pipe.
What people call the "suitcase" is the single center muffler on the early Challengers. The resonators are simply the resonators, which is what the tips mount to.Your stock exhaust has a ball and socket connection on the outlet of the resonator (sometimes called the "suitcase).
Solo makes some, they are not round like the ones you have, though.Can you give some exhaust tip that can be fit to my stock exhaust