OK, the factory manual shows that a code 26 can mean a high resistance condition on either injector 1, 2, or 3 (this applies to all the 6 cylinder sizes of that era). That is right out of the FSM. I don't know how you tell if there is a problem on 4, 5, or 6 unless you can assume that the manual mean't for you to interpret that 4,5,6 was a continuation and they just didn't want to print it. The same goes for code 27 which just means that the injector is not responding to the control signal.
A noid light is just a neon 12 volt light. These take only a tiny bit of energy to flash and they give you a visual look of what the injector is doing. When it flashes, the injector is firing (opening --- supposedly). You can do the same thing with a regular test light by back probing the wires to the injector.
I recall some earlier posts about how hard it is to access the injector connectors on the 3.0 so it might not even be possible to get a noid light on this engine. You may have to remove the intake plenum to do resistance tests. By inspecting the plugs, you may be able to see one plug that looks very different from the rest, and that would be the clue to a non functional injector. Some people have reported removing a plug wire one a time and when they get to the bad injector, there is no change in how the engine runs.