2) Apply glue to the contact areas of these two 2 x 3 reinforcements.
4) Using four 3" Sheetrock screws each for each upright joint reinforcement drill 4 clearance holes. Two each side of the vertical uprights and two in each of the reinforcement 2 x 3s. Then drill pilot holes for the screws. It's best if you do only one at a time. Drill only one clearance and one pilot hole at a time, then install and tighten that screw, then go onto the next.
This exercise will reward you with strong and stiff uprights.
Once the glue is dried or cured, you can back off the pivot screws to the point that gravity will move the swing-arm.