Interior rail identification and placement.

First off, thank you guys for unknowingly helping me restore my cars interior! I’ve used several threads from this site to help me figure out some head scratching moments. One in particular was hit to remove my dash cap. That was a pain, but made possible after reading a great thread on it.

I tore apart my interior hastily a while back and now I can’t figure out where an interior rail goes. I’ve tried dry fitting it all around the car, but I can’t seem to find where it goes. It’s a slightly curved 41” piece of 1/2” angle iron painted black with 8 screw holes running along it. Any help would get appreciated!

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