Stick with the crank sensor alone for the time being. You set the injectors to fire sequentially but they will not be in phase with the engine, but this does not matter as long as you inject when the inlet valve is closed. The inlet is closed when ever the coil is firing (as the cylinder will either be on its ignition or exhaust stroke) so in the case of a 1, 3, 4, 2 engine
Ignition occurs: 1&4, 2&3, 1&4, 2&3 ... so injectors will fire 1, 3, 4, 2 ... or as you don't have the sync pulse from the cam the engine may be firing in the sequence: 4, 2, 1, 3 which isn't a problem as the ignition still remains: 1&4, 2&3, 1&4, 2&3 and the injectors will still fire onto closed valves.
Does that make any sense?