There has been a good discussion about aileron gap seals on the Facebook Monocoupe Aircraft Group.
Here is a picture of the aileron gap seals on Cam Blazer’s Model 90A:
Dave Hawro posted several pictures of his (off the plane). The consensus is thickness of 0.020 2024T3 aluminum. The short vertical side screws into the aileron false spar and is notched to allow the gap seal to follow the curve of the bottom of the wing.