I dont' think cars shoud be allowed on the street without sway bars. Adding a rear bar will make the car more likely to oversteer (rear end stepping out). The trick is to balance the front and rear bars, A 5/8 bar on the rear is great as long as your have a 1" or 1 1/8" bar on the front. Too stiff a bar on the rear with the puny stock one on the front could make the car very loose. There are a few different ways that they might mount...most mount the bar to the rear housing and the ends mount to the frame rail via soem end links. Others do it the opposie...mont he bar to the raisl and the end-links mount to clamps on the springs.
1970 Fastback, 4V 351C, various colors with black interior