WEll, are you running a 5-speed or a Auto. Eitherway first you will need a better clutch or higher stall converter. Gears, Tubular Rear End components. Subframe connectors, and better tires.
Now that you Chassis is capable of it if your short block is in good shape you will need a Heads/Cam/Intake swap. Ram Air, Pulleys, Larger Fuel Pump, Long Tube Headers, full ignition upgrade, and a custom tune.
Or Drop the heads and cam keep everythign else and run the Good Old N2O/Supercharger/ or Turbo.
__________________ 2006 Mustang GT in Torch Red
C&L Intake, Evolution Performance Tune, Borla Axle Backs, Hurst Shifter, 4.10's, JBA Long Tubes, Prothane Engine Mounts, Steeda UDPs, FRPP Charge Motion Delete Plates
84 Bronco, 302 C6 on 32 10.50's | 
What does it take to get an 1989 5.0 Mustang into the low 12's. 
