Managed to get the photos a bit out of sequence, but you should be able to get the gist of my cylinder technique. Now a shot of the seat with the main support columns attached, and the seat assembly in place on the cockpit platform.
One item for designers to consider. The support column parts are laid out as identical parts. That means that, if you position the part so the seam is hidden on one side, the seam will be visible on the other side. It would be much better to lay out the parts as mirror images. That way, the parts on both sides can be positioned so that the seam will be hidden from view.