I asked Whiteline if my old rear swaybar and ALK off my WRX will fit the STi. Here is the response.

Hi Jim,

Thanks for your e-mail.

the ALK will fit the new STi.
The rear HD mounts will also fit the new STi.
But the rear swaybar is different. We have a new part number for the rear:
BSR37 = 22mm
BSR37X = 24mm
BSR37Z = 20-24mm adjustable.
BSR37XZ = 22-26mm adjustable.

The front swaybars are the same.

I hope that this helps.
Regards

Bob
www.whiteline.com.au