There is a trick to removing the window cranks on the Datsun 240Z (and probably most Datsuns). It can be done by feel, without damaging the door panel – with a little practice and the right ‘tool’.
The images below are the ‘back side’ of the window crank – the part that sits against the door panel.
Here is the detail of the small clip that holds the window crank onto the regulator.
What is cool about it is when you re-install the handle, you place the clip as shown then push the handle onto the shaft, and it snaps into place – no tools needed!