I just replaced my stock mid body mufflers with Dynomax Ultraflow Welded mufflers. I left the stock resonators in place.
Stock exhaust pipe size on my 2011 R/T with auto.. 2.5 inches down to the X pipe, and then the X pipe to the tips is 2.25 inches.
I believe the two stock mid body mufflers are about 17"x 9"x 4.5" case size...
I wanted just a bit more sound, and no drone and not too loud. This is exactly what I got with this mod. I read too many posts that said deleting the rear resonators caused too much drone, and quite a bit more volume.
I definitely hear the difference with the Ultraflows (pt 17222), a bit more volume and lower tone. I'm sure for some, it will still be too quiet, but for me it worked perfectly.
The Dynomaxs are 14"x9" case size, so a bit shorter. The muffler shop just added some pipe and they fit fairly easily. Hop this helps.