As mentioned, you can just change the muffler like many of the 5.7L guys do. Both the V8 & V6 trucks have single exhaust systems, the difference is the 5.7L is "faking it" for cosmetic reasons. The Hemi has a single downtube from the cat just like the V6, however it uses one muffler that has an exit that connects to a y-pipe for that twin tail pipe look. You can do the same as well if you like or just keep the single out.
I like the Flowmaster Outlaw myself, but their are plenty of different mufflers available to create that custom sound you want. I would contact a good muffler shop and get their recommendation. They will be able to quickly figure out the proper muffler to match your stock exhaust piping. Flowmaster and Magnaflow all have different tone mufflers in all the main tubing sizes. Then have them custom weld it in place. Should cost you no more than $275 - $300.