BYE-BYE had no quarter windows front or back, but it was not a simple task at all.
This is the best picture I have of it to hand, where the one-piece glass is visible. Both the front and rear modifications have had to bring the edge of the glass inwards slightly to provide sufficient channel (as Ken mentioned).
The reason the original rear quarter-window exists is because of the wheel-arch shape in the bottom of the rear doors. You can see in the close-up that there is an edge at the rear of the window frame to give the glass some rear channel. What isn't visible is the box-shaped section in the trailing edge of the rear door (outwards) and in the wheel arch (inwards) to give the window room to fully wind down.
Hope all that is some help.
cheers
RET