I have installed 3 different wiring harnesses in my trucks so far. A painless, ez wire, and a summit brand one.
I personally think the painless is overpriced and the only thing you gain is the firewall bulkhead is 3 piece like the factory one. I really like the EZ wire one I installed in the 67, it is like the Summit one and does not have a bulkhead connector and gives a cleaner install. I filled in the factory hole for the fuseblock and then drilled a 1" hole in its place with a bushing for all the engine compartment wires to pass through.
The bad thing is if I wanted to pull the front clip, you would have to unplug all the connectors. I dont really like the summit one since I got the one with the mini fuses and the diagram of what fuses are where is on the lid, a real pain when I accidently mis-placed it.
All of them have labeling on the wires every foot, and were pretty much identical other than the fuseblock unbolting on the painless.
All were made with quality wire.
Dont think that the painless is a plug and play like I originally thought. It is just like the other 3 brands I installed, they leave all the wires long and all have to be trimmed down to fit exact. All light sockets have to be installed, I think all that comes with them is the headlight pigtails and the headlight switch pigtail. All the ignition, gauges, heater, side marker, turn signal, tailight sockets and other misc connectors off the original harness have to be used.
Just dont throw out your factory harness until you have 100% installed your new one, you have to re-use the heater wiring, wipers and some misc. I soldered all connections and heat-shrinked them. If I were to install another on I would go with the EZwire as it is a little under $200 vs the $500 for a painless.
http://www.ezwiring.com/wiring_harness.html
Thank you for your service and stay safe!