I believe that you completely remove the thumbscrew (circled in red on photo), and with the belt off of the handwheel, tip the machine back slightly, and lift the machine up. It should slide off of two hinge pins inserted into the rear of the machine head. There usually aren’t any grub screws to loosen on these hinge pins.
Your empty cabinet top should look like the photo of mine when the machine is out. Be careful when you set the machine head down on a flat surface. It may not want to set up straight, and kind of have a rounded-bottom feel to it. They weren’t all built to set on a flat surface.
CD in Oklahoma