I finally got around to fitting the wipers. The wiper boxes need to be fitted at an angle so that the blades sit properly on the screen. I used the chrome cover to get the angle of the pilot hole. The shaft is 16mm but given the angle needed I used a dremmel to gradually open the hole to right size.
Looking good. Malcolm told me that you didn’t actually need a screen, wipers or washer jets for the IVA, and that it might be better to leave them off because there would be fewer things to fail on.