Which ones are long enough to reach your spring eye to actually work? Most come up short and the front snubber hits before the spring eye.
Measure from the center of the rear plate {If there, use the center locating hole for the pad} to the center of the longest hole where the front snubber bolts into, then measure from the center of the axle tube to the front spring eye and see what you need to put them in the right place. Mine is about 28" or so on a second gen Nova.
Dave
67 Nova Boy
http://www.how-to-build-hotrods.com/traction-bars.html