1. Assembled and test-fit the aftermarket "blind hinge" to verify where it will be located.
2. I decided to create the oil door out of aluminum instead of fiberglass. I cut a piece of aluminum from the unused baggage door skin cutout (since it already has roughly the proper curve to it), then traced the shape of the fiberglass oil door onto it. I trimmed and sanded it to a nice even shape, then test-fit it on the cowl. It's not bad.
3. Used a Dremel tool with a cutoff wheel to cut out the oil filler access opening in the cowl.
4. Sanded and filed the edges and corners of the opening.