I did an air conditioning job and I wrote it up - the first part was pulling the instrument cluster. Here is a link to the write-up on my site:
http://www.funnyyouasked.com/Mercedes/W126/ExpValve/removal_and_replacement_of_expan.htm
Go down and you'll see the tool you need - don't make it, it's cheap enough to buy from a dealer, but I provided the dimensions anyhow.
I would recommend strongly to put some scotch tape or something protective on the wood (use something that comes off again afterwards!). There is a photo on the writeup of the cluster coming out.
Good luck - doing it right only takes about five minutes!