E39 Head Unit install

I know its getting a little long in the tooth, but my '03 540i/6 is a pristine example that I plan on keeping for awhile. So, time to upgrade its electronics. I bought the bezel kit from the German fellow on eBay, and its well made, but it is a little hazy on how to cut/modify the air duct behind the radio. I've searched the boards but can find little on this, and no pictures. I will take pics if I do this, but looking for someone who may have already so I don't need to reinvent this wheel. Appreciate any help on this.
Mike