63 Dart exhaust system recommendations

I would strongly recommend stopping by your local muffler shop and getting a quote. I was considering getting a TTI system for my 69 dart at about $700. Turns out the muffler shop could make a custom system for 550. This is from headers to behind rear axle with an x pipe, granted a friend gave me the mufflers so that wasn't included in the price.
When you buy a kit online, what you are paying for is the ability to do it yourself. A muffler shop has resources which allow it to operate with significantly lower costs.