[HO455]

If you have any doubts about the tail light harness I recommend replacing it before replacing your headliner. That is if your original headliner is bad. If you are lucky enough to have a nice original then the decision is whether to repair the bad areas or to make and install a replacement harness under the body along the frame. Personally I would go through the work fabricating an under body harness and installing it before I took the risk of damaging unobtainable headliner pieces.
I have seen and inspected both AAW and M&H harnesses. The are both quality products. I have the AAW harness in my Burban (Yes, they make a factory style plug and play harness). My decision to go with AAW had to do with the delivery lead time differences. With pert-near 30k miles I have no regrets with AAW.
But don't get me started on starter switches!
If you do replace the tail light harness harness with an factory style harness I recommend removing the front seat to make it easier to access where the wires drop down from the A pillar.
I am still using the original engine harness, if you can call it original after replacing the ballast wire and converting to a later model SC alternator and wiring head light relays. At the time when I replaced the underdash harness I didn't have a real plan for what I might change in the engine bay. So basically evolution happened and it is what it is now.