Alan, welcome aboard. They treat the 318 like grandmas Sunday church engine? LMAO, no surprise there and for a good reason since the Charger is a good bit heavier and longer than most A body cars but worry not!
Adding some power to that engine is easy. However! Do not expect much. It can be made enjoyable.
Now about headers, there are 3 choices to choose from. The first two I'll mention are expensive but worth the cost.
TTI and Doug's headers.
The next one I'll mention have a few cave eats. There the one size fits all header made by everyone including the local nut case that is probably dropping acid and smoking meth right now around the corner from you.
He may actually make a better pair than some of the other major places do, depending on what day the major market places made them on and if they had a fight with the wife and/or are hung over.
Sometimes they fit great!
Sometimes they fit with a few tweaks of the sledge hammer.
I have had the cheap Summit headers fit better than the all high and mighty Hooker brand.
These headers have 3 tubes that run under the front drivers side steering linkages. Sooner or later, they hit the floor and sent up. Hit them enough, you'll wear a hole through them. Oh! They also love to rust out at the contact points!
Check Summit racing or Jegs for there exhaust kits. I used a Jegs kit on a old Duster of mine and it fit very well with just a little trim needed on the drivers side at the bumper. Get the 2-1/2 pile size for a performance oriented stand point. The 2-1/4 is good for very mild engine enhancements.
While they were actually designed for hooking up to Hooker headers, it is more than likely a minor tweak is all that is needed to fit it in with other brands of headers. An "H" or "X" pipe connection will need to be purchased sepreratly and spliced in. While it is not needed, it will quite the exhaust note down a few decibels and aid in power in a modest way.
Just be aware that header installation is a huge pain in the *** and a buddy, hopefully one that has done this before can lend a hand.