>>105656649
>Is that a metal lip?
Yes.
>Looks like a job for a high-gauge steel sheet nibbler and a bastard file. You might be able to swing it with just the file.
No, the door has an overhang like in >>105655739 that goes around the entire perimeter of the door.
The steel lip is there to protect against gas leaks as the gas line terminates in the corridor.