Jeff Kugel demonstrated the simple procedure on this Indy-style frontend. After removing the cotter pin and clevis pin, he lowered the control arms to the shock-absorber "top out" position, replaced the clevis pin, and took a measurement from the upper and lower mounting-hole centers. He raised the arms to "bottom out" position and measured again. He now had the lengths of the shock fully extended and fully compressed. On a traditional frontend, you'd use a jack to raise and lower the upper shock mount bracket.