Panhard, Diagonal Link, or both with ladder bars?

If you want to soften the race car ride you could replace the heim ends with a rubber bushed end like Detroit Speed and Engineering sells.

I would also replace the diagonal with a long rubber bushed panard bar.

If you decide to head to the race track...put the heim ends back in all around.

Still will not be a cushy as leaf springs but it will take 50-60% of the harhness out.