I doubt if Trooper torsion bars are much heavier than VX, if at all. The Trooper was sprung rather softly from the factory as a soccer mom vehicle, whereas the VX was more of a rally vehicle and probably had stiffer springs. I don't have any hard data to back this up, but that is my speculation.

I would look at the aftermarket torsion bars, they are 20-30% stiffer than stock IIRC.