While the seat back that comes with the Pinguino kit is quite adequate, I opted to purchase an Immersion Research Reggi seat back and adapt the seat back pillars to accommodate it. I have installed this seat back in my Impex touring kayak and like it because of its low profile and adjustability  However, my adapted installation of the seat back pillars is essentially the same as it would be in the original Pinguino seat back.  This video shows my adaptation and the installation of the pillars.

As you can see, I used a three foot level to set the boat level on its bottom and a smaller level ti pit the pillars in place vertically.  Also, because I had more material than I needed for the pillars as described in the manual, I doubled their thickness to give them more strength.

The Seat Back and Seat Back Pillars

The Reggi Seatback by Immersion Research