I am helping a buddy find some shocks for his rig. It is a '79 GMC 3/4 ton longbed with a heavy cummins sitting up front. We have swapped in a 56" 3/4 ton leaf pack out of a burb. He is going to order a pair of Furd towers to mount them to the frame. I have a few of questions: 1. How should we measure? Since we don't have the towers, much less installed. Do we need to wait untill they are installed? 2. Means of measurement: With the truck sitting flat on level ground, do we measure from where the upper part of the shock mounts on the tower to the mount on the axle? Then flex the truck and measure how much travel we need? thanks in advance.