If you have a rear sway bar, support it in place as well. Most guys remove the rear valance, but I found it worked okay to leave it in place as long as you unbolt the front of the leaf springs first for removal and bolted up the rear first for reinstall. Once you have eveything back together, be sure to only hand tighten the front and rear bolts until you have the weight bearing on them.
Charlie
70 Challenger
69 Camaro RS