Good full penetration welds, rather than weak little tacks all over the place, was used to weld it into place. Pre-stretching the edge meant it pulled back flat after welding as no hammering could be done. Now you see the latch in place behind the window channel. Problem to solve now is to connect the door handle at the top right to the latch link on the left, without going in front of the window channel where the glass will run in. Top view shows it a bit better maybe. Can make out the door handle link attachment on the bottom right which has to connect to the gold lever coming off the top of the latch. Cannot go in front of the window channel.
I thought I would build a hinge to go behind the window channel. Just using some 35mm SHS for the support and the hinge pin made from a 8mm bolt. Made some arms for the hinge from 20x3mm flat steel. I drilled them all the same to match link positions as gives me the option of a ratio change if needed.
I welded the arms to the pivot ends and have a 21* difference in them so one end sat low enough below the door handle. Also put a dog leg on the door handle side to get it to line up better.
Rather than having more bolts attaching the hinge to the inside of the door, or welding it in permanently, I welded it to the top of the latch housing. Made up a short link to connect one arm to the latch lever.
Here you can see it in place. Rather than go all the way down to the bottom of the door and back up the other side like you see others do, I thought this was a better solution. So now when I push the door handle button, it lifts the hinge arm up and transfers it to the other side and lifts the lever arm on the latch. The window channel and glass will go in between the hinge arms.