My bus rear looks similar to yours... Im a dognose bluebird...
It all depends on what you want to change or alter about the rear doors and glass.
I wanted to stretch the rear door so i would stop smacking my head on the top of the door jamb. But i did not want to change the rear window size. I didnot want to deal with finding new glass or blocking out those windows.
So i think the cut line was basically right behind the upper rub rail. there was some gross rust there so we just cut her right there.