Stop in for a cup of coffee
This is a '69 assembly. You can see all of the mounting bolts in this pic. The bolt on the short arm is part of the arm and shouldn't let the frame move up and down if it is tight. The part on the long arm is a non-threaded slider similar to a door hinge in your house. There is also an attachment at the top of the long arm up by the glass that also shouldn't allow movement if tight.
This is a '69 assembly. You can see all of the mounting bolts in this pic. The bolt on the short arm is part of the arm and shouldn't let the frame move up and down if it is tight. The part on the long arm is a non-threaded slider similar to a door hinge in your house. There is also an attachment at the top of the long arm up by the glass that also shouldn't allow movement if tight.