Is it probably the ECU?

Nope, nothing fancy. Everything is basically stock...wiring harness, grounds, distributor, coil, mech fuel pump. Only change was the ECU to get engine starting again. My question really boils down to whether or not differences in the ECUs would necessitate a change in ignition timing. I'll probably know the answer when a new replacement orange box goes back in. Was just curious to know in the meantime.