ORIGINAL: Montana Mike
Sorry I should rephrase that. The transmiion would be my guess. If the clutch bell, spur gear, and brake pad are spining and the dog bones are in the carriers, then my guess is it is something in the trasmission. And yes it is a pain to remove. You basically have to disassemble the whole rear end to remove the tranmission.
Yeah, I've been there. I had a runaway about a year ago straight into a curb and the chassis was bent. I had to order a new one and basically take the whole thing apart and put it back together!