How's the compression? I didn't see that anywhere in the original story. I've seen a few broken valve springs as well as a couple slight mis shifts that caused the rocker levers to pop off to one side of the can lobe. The cars both had good compression but it took longer to build the peak number. Removing the valve cover exposed that issue.
Another thing to check on the injectors is the presence of soot or build up on the top side indicating leakage in the head around it. Make sure that the holddown straps for the injectors are facing the right direction. One installed upside down can allow the injector to move as well and cause your issue. Keep us updated