Bob, pull the pin at the door bracket. The door check just pushes out, into the cavity of the A pillar. You may have to give it a tap with a soft hammer. You'll have to have the fwd trim panel off to retrieve it, and to reinstall. There is a spring on the check itself that holds it in place. Putting it back in requires putting the check in the closed position, and pushing it back through from inside. If you try to pull it through by the check arm, you are fighting the spring that holds the door open.
I just pulled one out of a '69 to verify the procedure, by the way.
Jeff