Due to variances in part dimensions, assembly tolerances, and tire sizes, the factory never specific a ground to fender lip height.

They did specify ride height by two measurements on the lower control arm, A - ground to lower ball joint and B - ground to t-bar socket. Subtract A from B and it should be around 1.125" difference. Although, I will admit, I do not have a '70 service manual to see if the TA/AAR specs are different from regular E body specs. I would think not since their rake was do to leaf spring and tire size differences.