Does anyone remember this edition of salvage squad when they restored a 407? This was 5 or more years ago and they accidentally cracked the windscreen of the car when restoring it and had to pay 400 odd pounds for a used replacement from the factory which suggested they were unique. It may not be helpful for a 411 but it might still be informative anyway - surprised the link to the whole programme works still!
click on the web link
http://www.arnolt.com/main-frameset.html
Then go to resources, then click on videos.