You have to remember basic physics - for every action, there is an equal and opposite reaction.
Basically the load that is being put on the front of the car by one of you torsion bars is causing the opposite side of the rear end to sit higher than the other. Without your shocks and with no engine and tranny, there is nothing to equal out the torque that is being applied to the body. Once you get everything settled in, then you will need to adjust the torsion bars to make the car sit level