need more help

get long tube headers, O/R h pipe. The gear depending what you have a 5speed 3.73's auto 4.10. If the car is auto you'll need either the diblosport or SCT tuner other wise for a 5 speed its a speed cal.. if you do run side exhaust you might have to buy another bumper, and i dont know if you can use the flows for side exit

03Ghost told you all you need to know, but I'd really suggest 4.10s for a 5spd. We've got both (3.73s and 4.10s), and wish I had 4.10s in both.
You won't be able to use the Flows you have now for side exhaust...for side exhaust, the exhaust gases do a U turn in the muffler, so they have to be designed as such - with an entrance and exit at the same end. Flowmaster may sell such...I dunno.
CDC sells good stuff, but at a price. Spintech also makes a side exhaust kit. And jeez, if you want the sick, sh1t your pants sound, Spintechs baby...!
http://www.spintechmufflers.com/spintech/spintechindex.asp

Oh, and, yep, to make the conversion complete, you'd want to pickup a V-6 bumper. Ck out --> http://www.stangparts.com/

Exhaust sound is a very opinionated subject. What sounds good to one person may sound like crap to anther person. Head over to www.mustangexhaust.com and register (it's immediate activation and 100% free) - there you can listen to all kinds of different exhaust combos and decide for yourself.
With that said, IMO, the H definately has more growl, whereas the X is more of a scream. The H is often defined as a classic muscle car sound - and that's pretty accurate.
As far as a tuner is concerned...I believe in SCT. This is a very opinionated subject as well. One of the most important questions you'll need to answer is What do the custom tuners in your area use? - Typically, it's either SCT (Superchips Custom Tuning) or DiabloSport Chipmaster Revolution.

you will be able to use your flowmasters because thats what i did on mine. i just went to a shop and asked them if they could do it and they said yes i also have a dual borla tip on it, looks nice