I just finished putting a 21 circuit EZ Harness in a 73 307 stick car. The next time would be much ezier, but still not EZ. It didn't arrive with instructions, and only a few connectors.
The ingition switch wires, turn signal switch wires and the dimmer switch wires are already terminated, you just have to finish them off.
The rest of the harness is very high quality, and the wires are labeled every few inches so it is easy to trace them, but as said, it's not a plug and play.
I would never have gotten it to work if I didn't have a copy of a factory wiring diagram, with circuit codes. Even with that, it was difficult because EZ uses different circuit configurations than the OEM, and my mind wanted to wire it as OEM.
This would be a great harness for a hot rod or for a car that was customized - I think what made it hard was trying to get it to match up with OEM stuff like the connector for the instrument panel. The different circuit layout made that pretty confusing, and even though I've done quite a bit of wiring, I had to walk away from this one a few times to let it soak in.
I should say though, that when I put the battery in it this afternoon, everything worked like it was supposed to. I haven't figured out how I'm going to mount the fuse box - it looks just like a GM, but the way the wires come out of the back, you can't mount it to the original mounting holes.
If you decide to go for it, I would be glad to share more to try to make it EZ for you.