@Blair Vidakovichrecently added a great page to the #Hackaday TTLers:The Electronics of IBM Standard Modular System Logic

He reviews the individual ECL gates of SMS modules and they are pretty simple :

Compare this to the "early ECL" diagram I mentioned earlier and see how they match :

Unfortunately, the IBM way has 4 power rails (with 6V differences). That's a LOT, and a significant waste, but at that time, transistors were very expensive...