
Remember that while you know rusEfi timing advance (sparking angle from TDC) once you look at the console or TS gauge, you do not know OEM timing so you still do not know true TDC offset. Do you have OBD connector on the OEM harness? Can you use something like Torque for Android with an elm327 device to see what is the OEM timing? Or maybe there is some mark on the engine you can use with a timing light?
But even without knowing TDC position you are good enough to at least idle this engine with rusEfi spark control.