You can probably put 18s on there without any issue. My buddy is running 18x10 in the rear, and 18x9 in the front on his sn95. American muscle has decent deals on wheels and tires.
1986 GT with the typical poor boy mods. 3.73s, Hurst short throw, King Cobra Clutch with aluminum quadrant, lowered two inches on Eibach springs, Hopefully adding some heads and a decent intake soon!