Shock Question

[western star]

Dropped my 71 down 3" in the front and 5" in the back. I've taken the standing measurement and I have 13" between the rear mounts and 11" in the front. My question is how much travel does a shock need. I figure around 2" up and down. When I jump on the truck up and down without shocks it's only going down 1" to 2" maximum ( watching the rear rubber snubber coming down to the axle) Not sure how to ask for the shocks at the auto store. Any help would be appreciated.