Update has been a long time coming, but I changed channels along the way.
The AMD quarter did not fit near as well as I was led to believe and I went looking for an NOS. TravlnZ28 came to the rescue with a nice one and I drove to his place in TN to bring it home without the shipping gorillas getting a chance to destroy it.
Here is a pic of the door gap with the AMD. It is way too wide and the lazy curved edge didn't help either. The seam at the extension panel was the same, wide, lazy bend and the lip at the trunk lid would require cutting, repositioning and welding to look right.
The NOS door gap, WAAAAAY better and once I lift the door at the front, it will be even top to bottom...
Pic of the seam at extension panel, super nice. Unfortunately, I need to replace that too and the bends on the repro are lazy and the corner is rounded, not pointed as seen on the original. That will take work to correct, but I'm considering brushing up on my decades old brazing skills and using that to build up the corner.
Once I had established that I was MUCH happier with this piece, I used drill screws to hold the door edge in place and inserted the reinforcement bracket inside the panel. I had used drill screws to hold that in place while I drilled out the spot welds, so I was able to get that back in the correct location.
I then used 3 drill screws thru the skin to hold it tight to the brace and removed the quarter.
Once I had it off, I used a silver marker to color in the spot weld drill holes and sanded the EDP off for welding.
Then it got welded to the quarter. NOT pretty welds. The brace gauge is much thicker than the skin and with the galvanized coating, made the welds get too hot to run a full circle without stopping.
On the skin side. I do have some overheat high spots and the 3 drill screw holes to knock down, but it will be fine with a skim to blend after that. I probably should have tried to set up my spot welder for this, but that can take a LONG time of experimenting.