like the deuce said the new v6's have good power. the 4.0 is a great engine. check out
Super Six Motorsports to get some ideas there are stroked out v6's out there that run low 9 sec quarter mile times. if i were you i would start with a cold air intake,sct or diablosport preadator programer, and a dual exhaust kit,underdrive pulleys,and mabey a set of 3:73 or 4:10 gears then you will be well into gt terirory. also the dual exhaust will require a rear bumper change which is very simple. check out
OEM Parts & OEM Wheels - Original Equipment Parts from NewTakeOff for your bumper, they are new, you can get the color you need so not painting cost, plus they are only 160.00 bucks. you may also want to go to
Ford Mustang, Mustang Cobra & Shelby Mustang GT - 5.0 Mustang & Super Fords Magazine and order back issue october 07 it shows a chick with a supercharged v6 running mid 12's
hope this helps some and good luck with your v6 stang