I've fitted the wiper wheel boxes today and can confirm that you need a 90/95 degree gearbox and you do have to shorten the wiper blade arms.
You also have to bend them to get the blades at the right angle
I've stuck a load of pictures on my Flickr site....
http://www.flickr.com/photos/peters-bmwmarlin/
next i've got to fit the motor unit and measure up for the bundy tubes....