But, don't I see two rigid bars going from the rear axle to the frame to the rear??
Its 2 in the morning, so I am a little fuzzy, but those bars are not in the same plane as the axle like the radius bars on a front coil setup, so the distance between the ends has to change as the axle moves up and down.
Which means with just the front bars, the axle would move back and forth as the suspension flexed.
Which brings in the rear bars which will not let it move back..............Sump'uns gotta give........