If you have a Stovebolt era truck the process is the same except the pin you push in is on the side of the cylinder. You must remove the cylinder from the dash to access it.
A 1950 truck would have the type of ignition switch like the picture i posted. It has the release pin in the face of the cylinder. You can see the plunger on the switch body in the picture at about the 10 o'clock position.
Here's a pic of a 54-55.1 ignition switch body, and you can see the plunger on the front as well.
