The seat back is attached using an aluminum hinge RS-80702. This was easily cut using some side cutters and the disc sander did a great job rounding the corners. Grabbed some nuts, bolts and washers from the local hardware store and it looks great.
I used my handy metal punch to put the bolt holes in the hinges. Once I marked all the hole locations I used a center punch to mark the holes. This made it easy to align the punch.