After reading the advice of various builders, I decided to strengthen the arm rests which I haven't attached yet. I used some alum. angle from the local hardware kindly donated by Chad Jensen. Did the layout, drilled, deburred, primed, riveted. Then clecoed in place (pic2).
You can see angle added to side flange of armrest.
ahrd to see with the reflections, but armrest with stifner clecoed on.