Based on the listed item in ebay, it seems the WRX/STI and our car (BM9) shared the same parts.
I also initially think we will only need adjustable lower rear control arm, however the more I think about this the more I worry, to adjust the camber to fix the negative camber, the rear lower control arm will have to be adjusted shorter than the OEM one. Once this is done, definitely the position of rear housing will change and not sure if the OEM rear toe and trailing arm will still fit exactly once this is done. But I definitely think it will lead to toe-out situation at the rear.
When are you planning to get this?