Techniques for fitting rear corners

[Nicolasticity]

Trying to get idea on the best method fitting or how not too fit the rear corner on a late bay 1979 Super Viking. I have noted that the rear corners were fitted between a closing panel and the rear side panel. I thought for a moment I could open up the seam and let it slot in but fitting the full rear corner panel from the back and then getting the flange in a gap just aint gonna happen!


So now Im thinking that I could cut some of the closing panel and then use my Snap-on pneumatic joggler to put a step in the rear corner so it sits more flush with the rear side panel. Does this make sense?

Heres a picture of how a joint might look?

in the suggestion you can see the old corner in the seam -

Recommendations welcome

Left side view of seam pf side panel and closing panel - some of the rear left corner flange has been cut out of gap

Left side view of lower seam no cutting of the rear corner flange.

Upper view of rear corner