Hello, this winter I went through that process, had to replace the whole metal sheet at the back of the car. As far as I can remember, I welded both of your gold marks on my quarters.
The upper piece (forgot the English name sorry) was it original or you also replaced it?
because I had to replace it, but first I installed my quarters then went for that part and had to adjusted it on the extremity with the quarter.
Then I welded it just like you on the trunk floor and then with clamps welded it on the quarters.
I will check tonight once I will be home but if you want you can go on my post in the project section. You will find it page 5, but the pics aren't big enough but we can see the welding marks.
Just click the link below (it is at the bottom of the page if I remember well) :
https://www.69roadrunner.net/mopar/threads/no-more-road-for-the-runner.12574/
Hope this will help you. Let me know if you need anything else
Thomas
