Yeh, I have a very basic rear end in my GTSt, not the sort of torque you have with the T67/RB25 but with 17" Semis my car doesnt wheel spin in 2nd let alone 3rd.
I would bin the LCAs and even the upper arms, if you still have the std arms then just throw a bush set in them. If you want I can send over a set of upper arms with adjustable bushes in them that you can trial.
Using std bits may mean your car isnt the quicket corner speed wise, but you wont be the slowest. And you can be assured the car will generally be well behaved. The slowest guys are the often the ones with all the stuff under the sun in them and as a package it just doesnt seem to work.
Hell if you ask nicely I may even send over a spare Whiteline front swaybar for you to trial if you want