ALK, diff/sub frame bushing r good start. further on, u can look into group n engine/tranny mounts.

As for bracing the weakest link is sub frames, most japanese swap rear subframe brace to a liberty one(straight bolt on, much thicker). And Jspeed fender brace and cusco hbrace (whiteline, ultrex ones block tranny drain plug) can further help things to be more stiff.

if i were u, i will skip the sway bar if u r getting coilover eventually, choose spring rate carefully though

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport