I've been pondering the possibilities still. I took a couple pictures tonight and that has helped me brainstorm a bit. I'm posting my thoughts here in the hope I'll get some constructive criticism.
If you look at the top view of the PH actuator up against the stock bracket, you can see that the outside edges of the stock bracket are almost perfectly lined up with the actuator. If you look at the side view, it is about 1-1/2" from the stock mounting hole to the center of the lower (right in the photo) lightening hole. That is the difference in length between the PH actuator and the stock one.
Here's my current plan A:
1. Cut the stock brackets at the red line. This will leave both front-side (top left in the picture) rivets and two of the four back-side (bottom row in the picture) rivets intact. I will lose the two lower back-side rivets.
2. Cut some aluminum, probably from a piece of angle, roughly in the shape of the blue outline. One piece on each side.
3. Rivet the new pieces on the outside of the stock brackets, using the rivet locations shown in green. I will probably put thin shim pieces between the stock brackets and the new brackets in order to ensure there is sufficient room for the flap actuator, which is just a hair (0.021") wider than the outside edges of the stock brackets.
4. Mount the PH flap actuator at the position marked in yellow.