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You will need more toe on the rear....the front also need to bring that caster back closer to OEM. When the suspension travels it will rub or hit the edge of the fender.
Based on what other with 4RS have done the 991 camber plates work. They add camber and correct the caster....much better than just adding shims.
Lowering the car can also add camber.
I have a Heigo half cage from my GT4 and it fits the RS according to the manufacturer.
Are you planning on installing one in the 4RS? Pictures if you do please?
I would gladly have given up PDLS, FAL, PTS, and a bunch of other three and four letter options if we could have gotten the Porsche factory titanium roll bar on our US cars. ;-)