If you can find light-to-medium dense balsa slabs 3/16" to 1/4" thick..it is hardly work the effort to build up the tail feathers on a small racer type model.
Figure your 70% Quickie wont have very much wood back there to begin with.
Take a gram scale with you to the hobby store when you select your wood. This will teach you how to recognize by eyeball which sheets will be light / medium / heavy. For practical purposes, I don't like to use contest grade [ultra light] balsa for planes like this unless you are carving out a thick block. I don't like heavy balsa unless it is for spars, stringers [longerons] and other structural items.
Medium weight is my favorite for tail surfaces with this general size of plane. You have some warp resistance and enough stiffness for a 14 inch span stab / elevator, plus the wood is just right for slitting hinge slots. By the time you "airfoil" a 1/4" thick tail surface, you've removed about 1/2 the weight but still have enough of the original integrity to withstand the forces of flight.