This may not be prescient, However my dad drove Imperials for years. He regularly add 500 to 700 lbs to the cars in clothing samples. His solution was to have extra leaves put into the springs. When the car was loaded it road evenly. When unloaded the car was about 3 inches higher. It did take about 6 months of this to even the car out.
Best guess: Bars are not indexed properly. First, release the tension on the torsion bar adjusting nuts all the way out. Then back the bars out and rotate 1/4 of a turn. Re-install and try again. NOTE: Under no circumstances should you crank the adjusting nut either way without taking the load off the front suspension by jacking it up under the frame.