Many people will replace the factory suspension anyways, so for them damage here is of little concern. If the stock suspension is to be retained, there are a number of items that should be checked. Check the spring packs for broken or bent leaves. If there are no shoulders on the bushings or the shackle pin doesn't appear to pass through the centre of the spring eye/spring hanger the bushings will need to be replaced. Check at theres no movement of the shackle pin relative to the shackle plate. Pre-81 stock shackles are prone to the pins working loose.
Looking at the condition of the U-bolt ends below the spring plate will give clues to the use of the vehicle. If the U-bolt ends are bent/scraped, the truck has seen some off-road beating. While looking under the U-bolt plate, ensure that you can see the nut and spring pin. The pin will sometimes break in the middle of the spring pack causing the bottom chunk to fall out. Replacing the pin requires removing/replacing the U-bolts as well.
Check that the shock mounts on the rear crossmembers and u-bolt plates aren't broken. Frame/axle mounted broken pins must be cut out and new ones welded in. On 40 series, the top front shackle mount pin will sometimes develop play relative to the shock mount tower. If that is the case, it can temporarily be fixed by adding another washer to the large-nut end of the pin, but will eventually require proper replacement which involves welding/boring out the tower.