Looks awesome! i dint think the 18's would look good but its perfect on a GT.
Your rears is very low so you may make some contact due to the very wide rubber. If you have an adj UCA you can prolly compensate a bit, judging by how low you car is in the rear you may need an adjustment anyway, are you Lower contrl arms parallel with the ground? My GT was low like yours, my LCA's were not parellel, the ADJ UCA needed tweaking.
Were you able to use the hub rings? I was NOT, there was not enough threading on the bolts to secure the wheel when the hub rings were used. Im getting some shimming betweek 55 - 65, im looking into getting them made for my application.
Congrats, car looks sinister.