Some points on re-assembly. Green circle shows the little ball and spring that are for the f-stop detent.
Blue circle is the notch for the screw that holds the anti-rotation spline assembly in plase and keeps it from spinning when mounting the lens.
Red circle shows what appears to be a missing screw. However, there is a screw on the other side, and this hole is covered with a dab of paint. This lens had not been disassembled before, so I think it is OK with just the single screw.