I have 17x8 with 12mm offset on the front of my 90 GT and 17x9 and 24mm offset in the rear. No rubbing.
For 17x9 in the 18mm....For the front I believe will rub. Or damage the rim. The inner lip of the rim will most likely slide against the lower control arm and damage the rims. But for the rear you'de be set. My 24mm offset in the rear comes very close to my stock rear kicker shocks for my axle. But does not hit them. 18mm might be a better offset.
(I know about the damage to the rims in the front because some Jackass at Discount tire rotated my tires...

...It did not say to..But they did. I drove about five blocks and went back and said WTF. The inside of my rims were damaged and scraped my lower control arms. They bought me new rims.)
The bolt pattern for 87-93 Fox bodies...is the same as 74-93 Mustangs.
Bolt Pattern is 4x108mm or 4.25"