[ChrisZang]

Hmmm,

the 986 S and 987 S have the same brake calipers and brake rotors, so they will clear the brakes for sure, so we're covered here

Now let's look at the offset

my wheels:
front: 7J 17 ET55
rear: 8.5J 17 ET48

987S 18" wheels:
Front 8J 18 ET57
Rear 9J 18 ET43

That means
the fronts have 15 mm more inner clearance, 11 mm more outer clearance
the rears have 1 mm more inner clearance, 11 mm more outer clearance

So yes, they will fit.

BTW: the reason why I am doing DE/TT on 17" instead of 18" rims is that track days tires wear fast and are expensive and 17" tires are significantly cheaper to replace than 18" (budget racer that I am)