I believe the '99 Cobra's may be able to get close to that. Maybe 5.6sec. stock, after the "fix". I think the '99 GT's are rated at 5.9sec. Those ratings in the back of magazines aren't the most reliable. In the 1/4 mile, I think the Cobra is capable of 13.9, while the GT can do 14.1 sec.
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T-Bones 1997 Cobra
Wht/blk, Pro 5.0, 4.10's, aluminum driveshaft, FRPP throttle body, C&L MAF, K&N, off-road H, Flowmasters, s/f connectors, FRPP pro springs, BBK caster/cambers.