As I have been fitting replacement steel wings all round I have watched your installation with great interest. As my car is a '79 the running board section of each wing had a few through bolts and plenty of screws holding it to the under side of the chassis/door frame. These tend to pull the panel somewhat unevenly onto the a narrow edge. I also noted from a recent Miscellany that later cars now have a "gutter" that the running board sits on. Looking at your pics I think I can see a similar support plate. If I am correct a bit of advice here would be appreciated.
I have also studied your Gemma steering box installation as in the past I did a straight swap with an original Burman but found the steering limited by the arm hitting the cross wire on LH lock. Another alignment job I've been looking at while the wings are off.

simon