I would swap the injectors first. If the problems still is there. Turn the ingition on and move the throttle and you should hear clicks from the bank of injector the trigger points are selected to 1/3 and or 2/4. You can rotate the distributor to select the other bank. You can then pull the each of the connector off to see if which one is/are clicking or injecting fuel. If it clicks it is probabley OK electically. You should get some resistance or <10 ohms (wire to injector and 3 ohms for the injector winding) from the ECU connector to the injector and back to ground on the manifold. If it is 0 ohms you may have a short in the harness or you have not zeroed the meter and or are on to high a scale. If the ECU is suspect you maybe able to extend the #3 line to swap #1 and #3 harness cables. I talked to one ECU repair guy and he said the solder joints are the only problems he has ever found on ones he has repaired. You can Oscope by back probing on the injector connector and comparing pulses to the working ones as another check.

Greg Bodner
1970 1800E