There is a flat machined surface at the front of the engine block, just below the front lip of the passenger side valve cover. It is actually the machined surface of the block right where the head attaches.
If your block is original you should see two seperate alpha-numeric codes stamped into the metal. I'm not exactly sure about '79 numbers, but I am pretty sure that the first code should include the last 6 numbers from your VIN as the last values in that code. The second code should start with "V" (indicates Flint engine plant) and end with a three letter suffix code that starts with "Z" (ZAA, ZAB, .....) This suffix code will ID the exact use of your motor (L82, L48,....)
If I have confused the heck out of you, locate the numbers on the engine and post them here. Someone should be able to translate them for you!
Mark