I may be wrong but a 87+ 5.0 is 225hp compared to 260hp for the 99+ GT, torque is basically the same. With a catback, h-pipe, silencer out, timing bumped, and maybe 100lbs thrown out of the car the 5.0 should have a very good chance. An LX 5.0 should also be about 250lbs lighter than a 99+GT.