For a bank to bank system, the ECU doesn't need to know where the #1 cylinder is. Every cylinder gets 2 injector shots per combustion cycle, one on the opening intake valve and the other 360 degrees later, much like a batch fire system. Where the spark goes is determined by the distributor and where the rotor is pointed so it isn't a concern for the ECU.
The Buick ignition module has a cam sensor input. The ECU simply sends out a pulse every 120 degrees to the module, and the module sorts it out from there. When the module sees the cam input, it fires the coil connected to cylinders one and four, and it "knows" the order from there.
Craig
