Basically you want a Cat-Back system.
It bolts onto your exhaust AFTER the catalytic converters.
(if you get a COMPLETE kit, you'll notice the pipes run from the Exhaust Manifold, all the way to the Exhaust Tips.....which means it DOESN'T leave room for catalytic converters.....it's assuming you aren't running any......but as you may or may not know, cats are a MUST in order to pass emisssions testing.....unless you live in a county that doesn't test for emissions.
Nearly all mustangs come with ATLEAST 4 cats, the newer ones probably come with 6!!!
I had 4 cats on my 1994 mustang
, I got the Pre-cats deleted, and replaced the remaining 2 cats with better quality High-Flows so i would still pass emissions.
(the pre-cats are located RIGHT under you're exhaust manifolds, those can be removed and replaced with Pipe, and you will STILL pass emissions.....although it is ILLEGAL in most areas, so dont rat out your mechanic!)
Here is an example of what you want.
(make sure that website is legit first if you are going to order,lol, i just yanked it off google real quick.)
But basically the H-pipe setup you want, will include.
-Flanges/Pipe connectors(might include this, maybe not)
-Rest of the exhaust pipe + Mufflers
-Hangers(may not come with hangers.)
I recommend just buying some flowmaster 40's, and paying a exhaust guy to make you a custom dual exhaust with 2.50 inch pipe.
if you find some mom n pops shop, they will probably do it for 300-600 complete exhaust.....which isnt a cat-back system, it goes from the exhaust manifolds all the way back, and he will just re-weld your cats back into the stock place.