efi is easier to work on than you think. I put a 2004 4.1L in my 74 260z and the efi is awesome to work on, so easy.
Were all the plugs that aren't firing on one side of the Block? If so then your not getting power to coil packs or injectors. The other problem could just be a map sensor or maf sensor. From the look of the plugs i would guess map sensor.