To truly settle the debate the answer to your question is "No". They were not a factory "Option". They were standard on all GTs from 87-93. You couldn't get them on anything other than a GT and every GT had them... except the 93 Cobra.....
2012 GT Grabber Blue Ported 2018 Intake, 85mm throttle body, JLT Carbon fiber CAI, Magnaflow O/R X-pipe, Roush Axle back, See "My Garage" for an extensive list of mods.
1991 Mustang GT 363
2016 Challenger SRT 392
2010 Challenger RT
2016 H-D Street Glide FLHXSE 117 stroker