Evan is right, or at least from the images it seems that way. Here is one suggestion you may not have considered. On parts like this often you can use 3/4" pipe type wood clamps and a long threaded section of pipe to pull things together. Get the ones at Harbor Freight...I think they're about $12 per set. They'll work fine for this. If they don't fit exactly (because of curve of door, etc) I've used two of them (two sections of pipe and two sets of clamps, that is) plus two pieces of 2x4 on each side of the door. Not easy to describe, but I'm sure you'll figure it out. Just pull them together well and oxy-acetylene weld or actually I'd flux and braze the seam (no sense in burning through and it is really easy to do that on this sort of sheet metal) and you'll be done. A brazed joint will be plenty strong enough. If you're careful, you can braze right up into the contour part and then file it later. Good luck!
