The floors inside are shot. The front of the springs don't look to bad
The fronts of the springs sit in that simple steel pocket, which is held to the floor pans with just a couple of small bolts. Under good conditions that's not a lot of support/attachment for a major drivetrain member. Take away the floor strength and your rear axle is free to slide.
Resize your pics to 640 x 480 and let us see what you have. If you have Windows XP, Microsoft Image Resizer is a good tool to use.
