Asking for input/help diagnose, not an a-body

In New England everything rots. My daughter had a similar issue. Main frame rails and control arms were solid but box that holds the trailing arm ripped off. Had to do some fab work and reattach. Not sure how your car is set up. Time to get her new wheels.

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The road salt is vicious around here, I'm scared of fully boxed frames for this reason. I'd be willing to buy a lift just so I can get my cars in the air for undercoating.