Agree completely with what Clint has posted and would only confirm that you need better shocks to control those springs, (KYB's are good) as your stiff springs alone combined with stuffed original shocks are contributing to your harsh/bouncy ride.
No need to worry about the four trailing arms at the rear when you lower the car, just the panhard rod which moves towards the passenger side.
Get an adjustable panhard rod from Whiteline, but make sure that you get the right bushes for it, tell them twice its an RA23, not 40, and not a Commodore, as the axle side bush I got with my adj. rod was the wrong size.
And thanks to Clint who helped me fit (read that as I watched while he did all the work) my Koni's and Lovells to my RA23.
Cheers,
Mitch.