Fitting is often easier on a coupe as there is something solid below the rear window to bolt into. The worry with the berlina is that the "B" post is so slender. The Florida concept cars were pillarless, being based on the Aurelia, so the Flaminia "B" pillar seems like a bit of an after thought.
I think I saw comment a while ago of someone finding a fitting specification for Aurelias and hoped something similar might come out of the woodwork for the Flaminia.