rear shock on Dart to short? (large pic)

unhook the shocks and see what happens. The only way the shocks could cause this is if they were completely extended and still holding the car down. Were the Hi jackers air shocks? Or did they have a helper spring on them?

If old shocks were air shocks or had an extra coil spring on them, then your rear leaf springs are likely worn out and need replacing. Take some pics of the rear spring from the side (with the wheel removed and the front and rearspring mounts and I can give you a better idea of what is going on.