I have a westy and did the same thing on the passenger side.

For the upper anchor, I located the existing plug, which is under the
panel and can be removed with a phillips screwdriver.

I left the plug in the d-pillar, fit a small nail or brad into the center
of it, and then pushed the panel back onto it, thereby creating a pilot
hole for drilling. I then used about a 3/8" drill to make the full hole.
Once the hole was drilled, I installed the bolt, anchor and spacer. Very
clean install overall.

So, I don't think a separate upper panel is needed.

- Kevin