Lowering Duster Question

My 1974 Duster sags a little in the rear compared with the front. I like the lower look and want to match the front to the rear. I read using the search feature that I can lower the front by simply "loosening" the torsion bar. Is the nut shown in the picture the torsion bar? If I lower the vehicle with this trick, are there any concerns about doing so? Alignment or safety issues?