I called Magnaflow manufacture today and the only cat back system for the 2013 Ram Hemi with dual rear exiting exhaust is the 22". They have an 18" but the exhaust would exit in front of the rear tires. I want to maintain the stock look and use the cutouts in the stock bumper. It would look rather silly to have the cutouts with nothing there.
I guess I am going with the 22".
I'll get some before and after videos