What model and year is your Challenger? Also, do you have a manual or an automatic?
The Flowmaster Super 44 muffler that you are looking for is part #842448 for stainless steel, or part #942448 for aluminized steel. Good luck!
I would start by installing magnaflow 11366 mufflers in place of the resonators, because the mufflers are a open straight through design that flow good. The resonators are the restrictive part in the exhaust system. I installed the Magnaflow axle back kit, and it sounds great with no drone at all.
out with the old... (well technically 8k miles lol)