I have a friend that owns a 93 5-Liter GT Convertible 5-speed. The mods are: timing adv, silencer delete, 4.10's, 2.5 o/r H-pipe, Flow 2 chamber cat-back. In addition to those mods, we also put a 10-minute tune up in it. Tires are plain jane hard radials. Are mid 13's possible?????