Back to the new hole to buff out parts of the circle which are not perfectly circular! Used a die grinder, and improved the circular cutout dramatically.

BUT of course I then realized I'd cut the hole too small. I'd inadvertently used the inside dimension of the doubler, rather than the outside diameter of the cover plate, which inserts flush with the wing skin. Groan. Moved over to the left wing, and cut in that side inspection hole correctly.

Thankfully I'd cut the Right wing hole too small; but not intuitive on how to (over) drill a larger hole without a center index (since the cutoout falls off as you complete the initial circle.) Answer? Gorilla Tape to the rescue. Took a cutout circle, aligned it carefully, and used gorilla tape to secure it in place. That stuff is awesome. Cut in half of the larger circle, moved the tape, and completed the new cut. Easy-peasy.

Then used a die grinder with a small 3M buffing wheel to better round out the hole, and fit the plates in place.