Hate to revive an old thread, but it seemed most relevant in the searches. I can't see the photo of that frame rail; but here's what a cement parking block did to mine ><
Photo Album - Imgur
I'm really sad right now.
This is on the rear passenger side, the damage is after the split between the front and rear frame rails.
I tried looking for pics of 180sx rails but could not find any, is this the piece that is not on them?