If you are running a standard computer then it needs to "see" around 12 ohms.
So if you are using low impedance injectors (usually around 2ohm or so) then you need a resistor pack. A standard Toyota one is simple to use, but any resistor of the right resistance and current capacity will do.
If you are using high impedance injectors (12 ohm by themselves) then you need no resistors.
The size of the injectors (cc/min) should bear no relation to their resistance. Also some (most??) aftermarket ECUs can drive low impedance injectors directly because they are really, really, really, ridiculously smart.
Hen