C-pillar?
I remember that build thread, especially
at Permalink #131 when we were both describing the Watts 4-Bar linkage.
The problem will be sealing well enough. That aeroform lifted when air got underneath the edge. A good all-around seal with strategically placed NACA ducts is probably what you'd be looking for.
Have a look at christofoo's example:
There is a 1" or 1 1/2" step at the C-pillar. That turns the boat tail into a wake filler covered in [attached] turbulence. If the liftback wraps around the C-pillar at least to a neutral angle it can retain whatever attachment you have down the sides with those flush windows.