What wiring harness?

I have 3 wiring harnesses, One from a slant 6 no A/C, One from a 318 no A/C, and a harness from a slant 6 with A/C. I'm swapping out the slant 6 for a 340 and got a complete A/C from a parts car. What would the best harness to use? Is the A/C wiring in the harness for the V-8 and just taped back? I'm not sure what way to go. Thanks