I've take the plate off and also found that one of the nuts was a bolt - oil starting coming out as soon as it came out.
It is on the left below.
You were right about the longer stud as well.
In addition, this round plate with a tube is sitting loose above, the ones I've seen on Youtube at least are sitting a bit higher on feet. I have probably knocked it, and the tube fits in the strainer so I can see where it fits.
There were at least 3 gaskets on each side, some fairly well stuck in.
Also, there is a crack running down the inner face of the sump...something has happened here
