Seems like many options have been laid out for you. There are many ways to resolve this. We can all agree your current leaf springs are too weak. Stiff shocks help too.

The solution with the least drawbacks is a pair of Super Stock springs and a pair of stiff shocks.

A pinion snubber remove ALL suspension travel on the street. As for the clamps, leafs want to slide. You need to clamp these hard enough to force them not to because they want to. When they do slide, the clamps wiĺl hold your car down after suspension compression and hold the car up after suspension compression.