what you have on your car is called a cat back system, wich is what it sounds, the system is new from the cat back. What the X/H pipe refers to is the pipes from the headers to the cats, in wich case you have a Y pipe. A true dual exhasut would be a pipe coming from each header and never connecting. An H pipe is what you are going to want to look at probably.
Take a look at this article
BTW this needs to be in General Mustang Tech.