The LS swap into my 4X4 got put off to build my daughters 72 nova. I ended up installing a 5.3 and a 700r4 into her car first. I contacted a company called Wait4me performance for the wiring.
http://www.wait4meperformance.com/.
At $360 was by far the best deal on the computer tune and harness modification I found. I sent them the computer and the stock harness and they trimmed the unneeded wires and tuned the pc to my setup, ie: cam, intake, trans ...
I sent off nearly every wire under the dash and in the engine compartment from the doner truck and when I got it back, the harness I was to use was seperated from the rest with easy to read labels. That 18 months ago and I just checked his website and it looks like his price hasn't changed. @ $360 nobody else comes close.