Who knows classic Mustangs?
I have owned several classic Mustangs. I currently (for last 12 years) own a '70 fastback. California Mustang is very good, although I prefer NPD because of the better prices they have, and depending on where you are in country, you will get your parts faster (they operate 4 warehouses around country). You can get all the replacement wiring from either of these 2 places, as well as most of classic Mustang suppliers around the country. You could get a kit from Painless, but these generally a re a bit universal, so you may still have some cutting, splicing, soldering to do, where as the reproduction harnesses will be a plug and play type deal.
As for the chrome, if you can, and have the money, rechroming at a good restoration type shop will give you far better results that buying new chrome parts. Also, nothing fits better than original Ford parts. The repro parts that are chrome sometimes suffer a bit with poor chrome quality. Repro chrome is a good for a driver, but it may not be as good as the original Ford parts. Cost of rechrome parts will be higher, but I think are worth it, plus it keeps the original parts on the car. But the turn around time will be longer to get parts chromed by a good shop, figure a few weeks, to a month depending on the size of the shop. If you can, get triple chrome plate, most durable and best shine.
Good luck with your Mustang