Boxster_S_girl, I think you must have misread the PCA rules. All the Spec Boxsters running with the PCA use the PSS9 shock.
Looking at the
2017 PCA Club Racing Rules, I see on page labeled "page 25 of 59" (page 28 in the PDF), SPB class rules, 4.E., says Bilstein PSS9 shocks.
The rules from PCA, NASA, and POC are practically identical. It's easy to build a competitive car that is legal in all three organizations.