On a 79 the vin plate is on the door jamb not the door.
The vin is stamped on the passenger side frame rail inside the rear fender area. That link that LilRed7879 has is what helped me with mine when I was looking at buying it. I haven't found a broadcast sheet in mine. I've read that in a lot of those trucks people found them rolled up and stuck inside the cross member or somewhere close to it!!