What size is the TB and plenum legs (to each bank manifold) on the 987 intake plenum? And is your goal to have an OEM type package or are you gonna go renegade?
If it were my build and I were sticking with OEM, I would use a 987 airbx, 3.5" intake tubing, 78mm or 82mm TB connected to a plenum that is 3.25 or 3.5" in diameter. A new Bosch 82mm TB cost me about$200 a year ago. The 996 plenums are 3.5" but are a straight T shape instead of the curved T. If you find an old DBW model they can be had for $25. For the intake tubing (from airbox to plenum) I would do it custom with silicone and aluminum to eliminate the resonator and reduce heat soak from the engine bay. That is as large as you can go physically given the space constraints and should be plenty for the engine and be will only cost$100 love you have all the angles figured out.
If you wanna go renegade, cut a hole into the trunk and do a short ram intake. Theyre loud, and lots of fun
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