^ Mark has it right but there is a little more to it in my opinion. Generally with shocks, you don't want to fully extend it to where it tops out or fully compress it to where it bottoms out.
If you are purchasing new shocks and are trying to decide what size shock to get, follow these steps. Jack one side of truck up until tire leaves the ground making sure rear spring is hanging free. Measure where you want shock to go. This is your full extension distance. Then, jack up or drive one front tire on a hill until the opposite rear bumpstops make contact...again measure where you want shock to go. This is your full compression distance. Subtract about half inch or 1 inch from each measurement (cause you don't want the shock to hit each end) this is your total travel distance. Then order shocks accordingly.
If you are using existing shocks...you need to fully compress and fully extend them manually and take those measurements. Then build new mounts or brackets to suit.
This is what I do when setting up my offroad truck and might be overkill for and old pickup like yours...but the general idea is the same and this is how to set up leaf sprung suspension properly.
Note: getting the compression is important if you haul heavy loads with truck. Cause you want the weight to sit on the bumpstops before it sits on the shock...that is a sure fire way to blow out a shock in no time.
Hope this helps.
Last edited by stove51; 10/30/2013 4:31 PM.
