Gerbert,
This is a common occurence, usually once or twice "per owner".
You have a two person job ahead of you; you need to use a long-bladed screwdriver; use them to press back the spring loaded latches which are mounted in the well on each side, and pull it all out. You might need to do this from both sides simultaneously. Depending on how this was done and how it is stuck you might need a bit of force to pull out that rear part. It isn't impossible, just a pain!
At a Mercedes Benz Club Concours this past September, one of the newly-restored show-class 280SL's had this same thing happen (with an unfamiliar owner); the owner was white with fright until I showed him how to undo it moments before the cars had to be left alone for judging!
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored