So I wanna run a O/R H was curious would the stock exhaust system off a GT would work?

 

all you have to do is get "cat deletes" which makes your stock H into an OR/H

 

And you'll still need to get a tune to bypass the error codes and adjust timing for higher exhaust flow.

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Well, assuming your info is correct and that you have a 3.7 V6 mustang, the parts I dont think will completely line up. I dont know what the underside of your car looks like nor do i claim to be accurate, but its a whole different engine setup and what youre wanting to do may not be easily done without the help of a custom exhaust shop. and running an off road setup, you would normally have to remove the cats. so a tune is required there. Good luck! let us know what you find

 

Lol I have a bama tune.....solo that's not a issue at all. And my state has no emission checks (know someone will make that comment)

My car stock comes with a X stock just FYI... the exhaust is smaller diameter then the 5.0 just by a little...