[84LX89GT]

A high flow catalyst H-pipe with a good cat-back system (like Flowmaster, Borla, dynomax, etc.) will give you a nice deep sound. A little advice.....get a kit that has a one certain diameter tubing throughout. Some kits offer 2 1/2" exhaust that ends in 3" tips which gives it a hollow resonant tone, that i believe sounds bad let alone on a V6, but that's just my personal opinion. The straight piping throughout gives it a deep muscular sound and doesn't sound hollow and resonant. If you go to a website by Mac exhaust, Flowmaster, etc. You can email them and ask them as to what they'd recommend for a nice dual exhuast system and what's required for a conversion. Some kits require the use of a new rear bumper cover for the exhaust pipes, other kits work around the stock bumper cover.
You can also go on the sound files on this site as well as other mustang sites and hear how certain exhaust sounds on different V6 mustangs. Mustang World has a lot of V6 mustang guys and there are V6 enthusiast pages all over the place.
Good luck,