Neeed Header/Exhaust Advice

Are You smelling an overly rich exhaust, Cat’s won’t cure that- it should still be a fairly clean smell at lower RPM’s..
If your A/F mixture is on par. I’d uncover why it’s so overwhelming..may be a Tuning error, to a bad F.P. Regulator, Timing, etc
Everybody’s taste for sound is different, jump on YouTube & listen to the people who have different exhaust combo’s/systems installed. If you have a Torch/Plasma/Sawzall, a MIG/ARC & a 4” angle grinder w/Cutting & grinding discs, you can buy pieces, save $$ by building your own. Get a Pipe expander & with careful planning, you can use the newer style joint Clamps- no welding required.
If I was going for a purchase Exhaust for an 01’, W/FI, no drone, more like a nostalgic musclecar, I’d go with Kooks 1-3/4 in. Tuned Headers and Catted X-Pipe Combo, and a 2.5-3” Borla Stinger S-Type Cat-Back Exhaust. Sounds GREAT on the 4.6’s.. you want more growl & louder?- buy an SLP loudmouth series 1.
IMO shorty headers are a waste of $$. No Hp/Tq increases, potentiates that drone we dislike.
If it’s a long term keeper Car, buy Stainless (300 series, many others- like 400 Series- Rust.) If Stainless is Magnetic, it indicates Carbon abundance in the Chromium & may Rust.
Kooks Headers are 304SS but Pricey; as are Hooker’s, but Tuned, & well crafted, an easier overall install. If you plan on keeping it, whichever you choose, buy a 303/304 SS Exhaust, no worries about Rust.
Good luck! John

There's no way easy or fast way to install long tubes. I would plan on at least 300 bucks for the install if not more. The mid pipe and cat back aren't too complicated. Don't forget you may need oxygen sensor wire extensions for the long tubes as they usually move those sensors way back at the collector. I would definitely get a dyno tune for long tubes. They make a real difference in the mixture by moving the exhaust much quicker.

Hi, I would ABSOLUTELY recommend you run a Wideband 02 sensor A/F mixture gauge to monitor your Air/Fuel mixture with a FI platform, optimal time to install one now, new exhaust system. Not expensive & also a requirement for a Dyno-tune, find out how rich it’s running. This AEM Gauge works well, have (4)...: https://www.americanmuscle.com/phantom-ii-airfuel-analog.html
Better rich than lean, but too rich can gaswash oil off cylinder walls, get in oil & wipe bearings, score bores, Pistons, accelerate Ring wear, etc..the Tune you’re running may also lean it out in higher RPM ranges. Or, you may have mismatched parts, or malfunctioning parts. Start with basics, when was the Car’s last complete time-up? Any CEL’s? Always smell rich- since acquired, or slowly get worse with time?
Fact is, you won’t know your A/F Ratio for sure without that gauge, but reading spark plugs is the old school method that will allow accurate insight. More on that, here: https://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm . I’d be fixated on that.
Wipe oil off the dipstick & smell for fuel. If you smell fuel, change it & get it Dyno tuned ASAP.
Mounting the Wideband requires drilling a hole, welding a threaded boss (or bung) into one Exhaust Pipe, in front of the factory sensor so that it does not get a corrupted signal. It also cannot be behind a converter because they will skew the correct reading. Can also be mounted on a LT Header near the lower flange. Should take 30 minutes while apart. I Do have some limited experience with JBA Headers and X pipe assemblies, Cat-back’s. A bit more alarmed by the Rich smell (sorry for the Adverb,lol!). If you install ceramic Cat’s on an overly rich Car, they can disintegrate. Your Mufflers May have an obstruction as well, you’ll know soon...ever spit pieces of material out of the exhaust?
X pipes are generally raspier and louder than H pipes and have been shown to provide slightly more upper end power than their counterparts. H pipes lower RPM gains & a more nostalgic tone. Read more, here: https://www.americanmuscle.com/mustang-h-pipes-vs-x-pipes.html
It IS correct that most exhaust systems are bolt(or Clamp) up. BEST bet is to contact AM or Summit, look at reviews, get info on systems that can be installed with no mod’s required with the wraparound Clamps (Not U clamps) don’t underestimate yourself..MANY are designed for a guy/gal in a Driveway/single bay garage with basic hand tools & a few Hr’s to a weekend, use the Car’s OE hangers. Only obstacle is the 02 wide band install, and the Shop can do that.
Save some $$ and do it yourself or with a buddy. LT Headers May be more involved, jacking the Motor May be necessary for some, others- not. Have a Shop do that, if you think it may be too involved.
Car will be much happier breathing through long tube’s, shorty’s do little for performance. Will sound better through the new exhaust system, and suspect you will gain a bit once you have it DynoTuned, once & for all.
Kook’s Headers have the best craftsmanship I’ve ever seen, the Catted X pipe’s included. The Borla Stinger, SLP loudmouth are 2 of the best sounding exhausts in my book, and the simple wraparound Seal Clamp install requires Jack/Jackstands.
I’m verifying some info on JBA’s newest systems, will comment again latest on Monday..
Hope this helps thus far! John