Today I got the RH fender off - I had to cut off one very stubborn body bolt, but it's done. After removing the heater motor, I did indeed find two numbers underneath. The first one matches the partial VIN on the cowl - 7L160971. There is another stamp underneath the hole, and this reads K22 R. What, if anything, does this second number mean?
I am becoming more convinced that the cowl tag is not original to the car. It's held in place by hexagonal flathead screws, not rivets, and once I got the fender off, there's even more gold paint where a repaint just wouldn't touch.
Am I correct in that a vertically-oriented rectangular cutout in the firewall means an AC car? One of the local Camaro Club guys (great bunch) mentioned this - and the cowl tag is non-AC. Furthermore, there's an AC dash in the car.
Well, the bright side is that this'll be a good story to tell once she's all done!