Quick update...
As Pete mentioned - It looks like someone has has cut a small access hole in the A frame at the bottom which was hidden by the footwell side carpet. They've also drilled through the inner casing at the bottom and attached nuts to the oversized bolts. So, three questions..
1. I'm assuming that by attaching bolts to the nuts it removes the ability to adjust the bottom door hinge?
2. If the captive plate has been tapped to take a bigger bolt, does it still need a nut on the end or can I remove them and retain some adjustment?
3. Is it possible to replace the captive plate?