Mag, thanks for the replies! I feel better knowing that the rivet wasn't there originally; I had a really hard time coming up with an idea of why it was ever there in the first place.
One more question: Have you ever seen insulation on the back of factory kick panels? I'm more of a '65-66 guy, and I thought those models came with insulation, so I assumed the '69s did too and ordered a reproduction insulation kit. However, what arrived in the mail is clearly designed for a '65-66 kick panel, and now that I've looked a bit closer, I can't see where my original '69 kick panels ever had any type of insulation. Seems like it would interfere with the fresh air vent if installed in the wrong place.