The whole point of flared guards is to accommodate wider tire tracks and offsets. The fact that you can put them on the Fairlady, but then it looks horrid as the wheels are tucked makes me scratch my head as to why Turn 10 even put them in the game in the first place.
They’re the stock flares of a 240ZG, you also get the 240ZG nose in the game. So the point of them is to give you the ability to make the car look like a 240ZG instead of a 432Z.