Ditto on what Mike said. The ECM should be in the passenger side kick panel. But, if it were behind the glove box I would suggest removing the cable from the right side of the glovebox so the glovebox would pivot all the way downward.
The ECM in my 79 TBI Elky was behind the glovebox...but I put it there.
I have heard of the term ECM before and guessed it's stands for the Engine Control Module? Do I have one on my 69 ELKY? if so where can I find it? I'm trying to hunt down the cause of a no start condition now and that might be my problem.
I'm not surprised. Most 1979 El Caminos did not have an ECM.
However, the first 5th gen El Camino to have an ECM was in 1979. It was used for the 231ci V6 with the California C4 system. (Computer Controlled Catalytic Convertor). It was only available in California, and only came on the 231ci V6.