Exhaust dosnt tell us much. Headers o/r h? How about k/n, or pulleys. Have you dumped the air silencer and advanced the timing? I ask all of this because it matters. If you do have all the above and pull the swaybar you can run 13.90s on street tires. No dr's needed.
What kind of shift kit are we talking about? Are you running a stock converter? If you've got a healthy shift kit and a decent converter, and you can do the 1-2-1 AOD shuffle shift routine, then you can get 14.5s no problem. I ran my buddy's GT to 14.0 with little more than what you have. Traction and your ability to shift right are going to be your big limiting factors.
Why not go to the track, run it, and find out? No sense in bench racing, its common knowledge that a 5.0 modded like yours is a 14 second car. That means 14.00-14.99. Too many other variables to be more accurate.
For sure dude, I'll be on the lookout for your car...unfortunately mine is still on jackstands and unpainted so I will be stangless at Carlisle for yet another year...I will be hanging around with raceoholic330 and his blown black '88 GT with polished 01 Cobra wheels so if you spot us say hey!