Try to remove the cross shaft which the handle and return spring fit on first. The gear teeth which mesh with the quill will likely be straight, so careful drifting with a brass or aluminium bar should move it. I cannot see which way it should go, but there should be clues if you look carefully. Also, there should be a screw to stop the quill rotating, probably on the right side of the main casting which needs to come out, and will provide another entry point for the Plus Gas.