I had a set of one inch lowering blocks on my '68. They increased the leverage the rear end housing had on warping the leaf springs while under hard acceleration. The motor generated enough force to permanently bend the front passenger side spring segment into an almost "S" shape. A replacement spring and the slapper bars took car of that from happening again.
The car did corner slightly better with the blocks installed though. I ended up taking them out once the springs settled a bit.
