i think they will be plenty strong,as long as they are mounted in some good strong blocks.i would even go as far to epoxy them into the blocks,so there is no chance for them to loosen.
I would go with some black socket head screws- 8-32 nickle plated stuff like you have pictures isn't very good. Grab some with pliers and see how easy they bend/ break. I install hardware all the time- and have boxes of 8-32 stull like that, and the metal is more like "pot metal" or Tin than steel.
Got the second wing hinged. Will get the batteries and receiver mounted. Then I think all I have to do tomorrow is put on the control horns and set up the radio.
Got the second wing hinged. Will get the batteries and receiver mounted. Then I think all I have to do tomorrow is put on the control horns and set up the radio.