Standard GT flares are also called 7"/9" flares, for obvious reasons.
The factory GTs ran that combination but used a 1" spacer in the front.
You can comfortably fit 8"/9" wheels under standard GT flares if you have the correct offset.
There were also 9"/11" GT flares available but today, you can only get FG replicas in that size.
You probably have guessed by now what size of wheels will fit those.
Again, the correct offset is important for proper fitment.
There's literally hundreds of threads on that exact same subject ...