Dai, it is quite possible that the entire avionics bay cover was removed, I have no idea really it just makes sence to me that a hindged setup is better in terms of maintenance where the thing is not lying on the ground somewhere.
But your guess is as good as mine :-)
As for the rivet lines, perhaps it is how the skin is attatched to the frame that looks (in this overdone scale) like fastners instead of actual rivets, Im just specualting...
Theuns
Those are fasteners that are removed via screw drivers. Dai