Jack the frame up to take the weight off the springs and axles. Just when the leaf springs start to separate and try to lift the axle, pry around on the shackles. If you see any side to side or up and down movement, they are worn. It really is not that hard to knock the shackle plates loose at this point. Back off the nut on the center bolt to the last few threads, then whack the plates loose (away from the pins). If you have the truck jacked up square and at the right point, the pins and plates will be loose and you can check each pin for movement. The plates and pins are a taper fit, so when going back together, tap the plates to seat the tapers as you tighten down the center bolt.

Joe

1937 Chevrolet Inline-powered Streetrod