Try putting an equal load on both springs & measure how much deflection occurs...

Or swap the springs side to side in the Imperial & see if the sag follows the spring or the car...

I know of a couple cars with frame issues that have been adjusted around to sit level but really need to go on a frame rack & be reworked...

"The Armies of our ancestors were lucky, in that they were not trailed by a second army of pencil pushers."