A guy here with the screenname "Stangonline" had 275's on 17x9's all around on his Fox. Might want to ask him.
Also, you could check corral.net if no one can answer here. IIRC, people have gotten 10.5's to fit in the back, and 255's on 17x9 is fairly safe on the front.
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'93 2.3L Notch: Open-Track Project
'00 3.8L: Heads/Cam
'01 5.4L Harley Davidson F-150