If you already went through the skin at the rear door crimp, you already have to weld that edge back anyway...so you might as well keep grinding! Take off 1/16" more than you need, and that will give you room for your MIG bead to reattach the skin to the door frame. I am assuming you have the earlier brass hinges when you talk of milling. They are not the strongest items to begin with. I just think you are setting yourself up for "unforseen consequences" if you start milling on them...
Good call John. I just returned from my garage and read your post. I did exactly what you suggested. I ground deeper into the door edge and went for the MIG. My biggest problem with the MIG is getting it set right, but this time, I hit it right on the mark. Feed at 20, power at 30 (Hobart 140). It was just right. I ground it back down again, put a straight edge on it and used various methods of squaring it and now I have my 1/8 gap at the "B". This after Randall's 2X4 to close up the "A". I'm a very close 1/8 all the way around. It's not perfect, but neither am I. Something to work with. Tomorrow it's the new Chinese Latch and Striker. Any tips here?