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The plexiglass lens that will be fitted to the hole is held in place by upper and lower plates.

The first picture shows the rivets in the wing skin holding the upper bracket in place permanently.  The second pictures shows the three dimpled holes that will allow for mounting the lower bracket with flush mounted screws.
      These two pictures show both sides of the lower bracket I made. The upper bracket was similar but didn’t need nutplates for screws since it was riveted on.

      All of these rivets are the flush heads and I backset them with just a hammer. Worked perfectly.