Oh yea! Old Tyme trick right there. Since the rear of the leaf springs only job is to hold up the rear of the car when your at launch, they actually hold back the cars reaction and abilities.
The other half of that trick is to install clamps on the front of the springs to stiffen them up. MP used to sell these clamps. Just a simple set of bolts and bar that are rectangular to cross the spring with holes on the ends to run the bolts through and tighten up.
