Done it! As dusk falls the windows are in. There’s only a couple of screws holding each one but that will keep most of the rain out. Tomorrow I’ll need to finish securing the windows and fit the flashing and then we will be water tight.
I’m really pleased with the way they look. They were never going to be pretty from the outside (this is the back corner of the house, so not too critical) but actually things line up quite well.