You mean the rear A frame that sits on top of the rear axle right?
You're barking up the wrong tree, very few of us have done anything to that part, even with serious mods.
The reason your ride is harder is 2 fold
1) your old shocks were goosed and your springs were tired. After as little as 30,000 miles suspension components are past their best.
2) to keep the car under control whilst that much further off the floor, the new springs are uprated, by about 25% typically. That's why it's better to fit new springs than spring spacers IMHO. The dampers are also uprated a little, but then the Armstrong ones aren't that bad actually, when new.