Ah hell did not see it was a V6. You could always go with cat backs to start off with. Then get another header and mid pipe setup. Stainless Works seems to be a pretty rare exhaust system on Mustangs in general. I have not seen another one in my are with a Stainless Works setup.
They only seem to have one X-pipe too, wish they had an H-pipe myself. Debated putting a high flow H in my setup. I like the H-pipe soud over the X-pipe and will to take that slight lose of power fom it.
Just tossing it out there but I would think if you went with an aftermaket dual exhaust systm. I bet you could run the cat back system if you run 3 inch pipe.
I would send a message to the Stainless Works rep. Been talking with them myself on possible setups. https://mustangforums.com/forum/memb...ess-works.html