[Mr70]

Yes they did.
Dealer #213 in Calif. is different then dealer #213 in Michigan.
You actually have the reminants of the hardest part to find.
Knowing your dealer # is 213 in Michigan is better,then just knowing your dealers zone code.That helps narrow down your search considerably.The fact that you live in this area also is a BIG plus for you.
I show Michigan had 3 zones...Zone 1..Zone 44..Zone 45.
I don't see any Dealer names coming up when I tried all three of these with your dealer number,but that just means they are not entered into the Web system yet.
The closest I could find for yours is Zone 44 Dealer 235 which comes up in the Michigan Clinton Twp. area,so you might try calling or visiting dealers in that area,and talking to the service writers.
This is not an exact solution though,as it is not unusual for dealers to change code numbers many times over the years.Even if they stayed put in the same location.
Try calling Chevrolet HQ in Detroit and find someone who will take the time to search the 1979 files,as well as some surrounding area dealerships.They have this info,you just have to find the right person willing to use their time to help you out.