So if I understand the problem better.......the car under acceleration rotates the axle up like they all do. Since the car is lowered there is no pinion snubber due to clearance issues.

In this config the car rotates the axle too much bending the spring just behind the front hanger.

You added the cal track type bar to the car and now it doesnt bend the springs.Makes sense since this limits axle rotation.

This is wild. I need to check my car over and make sure I am not bending anything as well.

Outside of a pinion snubber a stiffer front spring should hold the axle from rotating too much.

How much room do you have from the bottom of the car to the pinion snubber moynting pad?