I bought a pair of GT4 front ducts for my Cayman and they looked identical to the ones on my Boxster base.
If you want more cooling air, there is a curved duct that attaches to the fender liner at the radiator exit. Meant for GT3 and GT4 fender liners with mounting holes, but you might be able to drill a couple of holes and mount them. They take the air out of the radiators and direct it to the rotors/calipers. Increasing the holes in the liners will help as the GTX cars have screens vs slots in the liners.
In the rear, the 981S ducts fit the thrust arm vs GT3 ducts that appear to fit the LCA. The base did not have any rear cooling ducts and I added the S ducts to complete the brake upgrade from base to S plus GT3 MC and Goodridge SS brake lines.
My Cayman track car with front 380mm/6 piston calipers has a modified GT3 fender liner with the curved scoop and the stock air deflector and I have never had a cooling issue on the fronts. The rears (345mm/4 piston caipers) were a different story. I boiled the Castrol SRF brake fluid the first two times on the track. Besides the standard 'S' duct, I added titanium shims and a 997 GT3 L-shaped duct that mounts to the LCAs and put insulation on the rear brake lines due to proximity to the exhaust. Fixed that issue. The rear GT3 duct works only with big brakes, 345mm or larger.
Bigger rotors helps as to get the same stopping torque, less force (heat) is needed on the pads the further the pads are from the axle.