Wow Niel, you should buy a lottery ticket, finding 3 dead ECU's is rarer than a 4 leaf clover.
You'll have to be much more specific about what exact system you have, there's many different ECU's between 76 and 79, 75-76 std, 75-76 auto, 77-78 std, 77-78 auto, 79 std or auto and a California version of each as well.
What is your bus doing (or not doing) that makes you suspect the ECU?, it's the most robust component of the whole system and I have only seen 2 actual proven failures in the last 15 years out of hundreds that were swapped with no resulting change in the symptom.
