There was huge void above the rear trans-axle extending all the way up to the package shelf. Made a filler panel to close it up.
A friend who's eye and opinion I trust suggested I narrow the outer bead of the wheel rim. I had narrowed the bead some previously but took the leap and narrowed them further after studying more photographs. Glad I did! The wheel on the left is the newly modified wheel, the one on the right is where I was before. Narrowing the bead also has the effect of making the tire sidewall appear taller without increasing the overall diameter - win win.