Can't you just use a single trigger to synchronize the cam? What if you use a normal distributor as the sensor? Ground the center terminal, then use one of the four outer terminals as a trigger signal. Use a pullup resistor on the signal line and every time the distributor rotor hits that terminal, the signal goes to zero.
i'm not sure about the wiring of it but yes, it can be done with one sensor on the cam as long as it's missing tooth or has some means of knowing the location of the cam.