I did a complete wire tuck on my 260z a month or two back. It's very clean. What I did was run the entire main harness through the hallow fender frame channel(fresh Air passage). And moved all the fuses, and other units inside the car in the passenger side under the dash. The channel is the perfect size. You'll run the entire harness back into the car through the firewall hole, then use a long piece of coat hanger or I used a thick tubing, or cable, pushed it from the front through and taped the tip of the harnesses and pulled it through. You'll need to zip tie or temporarily tape up the main harness so it's as skinny as possible. Then run alternator, starter extensions.
I still have the battery in the front, just didn't want to do the battery relocation yet. overally no wires showing, and it runs just the way it sits in this picture. I also deleted a lot of wires I dont' need anymore, like A/C and EGR, ignition coil is moved to the front of the car, so nothing is in the engine bay.
I also cleaned up the fuel rail lines, as I made/bent my own out of some left over 240sx fuel lines I had laying around. Bunch of other little details and it makes the engine bay really clean. Keep it clean, SOLDER, heat shrink wrap everything, and use shielded spade connectors.
The spark plug wires are autozone duralast cheapo's eventually I'll make custom ones and route the plug wires along the front side of the engine making it a lot cleaner, but as of right now, it's damn clean and it will do. I will also make a fuse/relay holding board for all the units that I moved inside the car, so much to do, so little time and $$$$.
To save money I had to be innovative. I used left over 240sx parts, 300zx parts, and zip ties, and brackets from 240sx. The spark plug wire seperators are just white zip ties zipped together. Instead of using rubber hoses, I had left over hardlines, bought a tubing bender for a few bunks and measured and bent simple 90* degree bends and gives it a much cleaner look. I did tubing for the fuel, booster vacuum, and vacuum advance on the dizzy. It gives it a nice shape and no sagging rubber hoses everywhere..
I bought a hot rod vertical overflow tank which figs perfectly with the tabs on the aluminum and stock radiator, I shimmed the overflow tank with 2 "Stanley" sockes, you can use cheapo harborfreight as spacers. I believe 2 new 12mm chrome deep sockets, and bought two long M6x1.25 bolts and that was that. So cheap little mods that look good and you don't need too much money