I dont know if i would recommend this, as the fuel pressure could easily blow the injectors out, potentially spilling litres of fuel under pressure. If you leave the injectors in, and unplug the igniter, pull the cas out and spin it you should hear the injectors firing, or test them with a noid light. Are you sure all the earths are hooked back up, there are two from the loom to the inlet manifold. Also check for power between one of the injector wires on each plug and the manifold. One wire on each injector should have battery voltage, the other is a swithed earth. PS are they the same injetors that came out of the motor before the maniflod change. Could there be a possibility that the fuel lines have been swapped around on the fuel rail(seen this a few times)