Either bar will make a big improvement in handling; add a set of stiffer torsion bars, and you will have big improvement X2. I also suspect reinforcing the lower radiator brace tying front frame rails together would stiffen up the front end of these “A” bodies even more. I haven’t installed lower radiator reinforcement to my car, but plan to soon.
I don’t know how far your plans for improved handling go, but consider installing new bushings, HD rear springs, sub frame connectors, and front disk brakes. If these changes are made your car will easily keep up with the modern iron, and be a pleasure to drive.