Please watch it 509lifted. We're here to help others with questions about the projects they're looking to do. It's highly likely that google just doesn't know how to bring up the answers or even the locations in which he might find answers to his question.
I know almost nothing about the 3.0L and 4.0L, but to start, you will definitely need the motor and transmission. Sticks of dynamite will do you no good, in this case.
The wiring harnesses will probably be very similar, but a more v6 experienced person will have to chime in on that topic, as I cannot offer further comment.
The a/c system should be able to stay in place, untouched by the engine swap. You may have to disconnect it while you're swapping motors, but through all the years of rangers, the a/c systems occupied the same space, except, perhaps, for the mounting location of the compressor.
Lastly, try to be as exact as possible with the questions you ask. Those looking to help you on here may give vague answers that could get confusing since we might not understand exactly what you're wanting to know. Nevertheless, don't hesitate to ask us to explain something further, if you're still not 100% following our advice.