[72lb4x4]

Be real careful welding on that long line or the skin will warp.

I think normally a flat faced body hammer and a flat dolly are used. Maybe the back of a heel dolly. I read once of someone using a rubber sanding block instead of a dolly. The rectangular kind where the part in your hand is curved.

The dolly goes on the outside of the door and the hammer hits the flange, folding it.

There are some welds on the inside where the flange meets the door.

Take your grinder and grind through the edge of the door skin. Think of the disc as the top of a T and the door skin as the vertical part. The door edge is where the two meet.

Then you can battle with getting the flange part off.

All this is hearsay, so wait for other opinions...