I would buy them raw. Make sure everything fits. Do the fab if needed. Then they can be ceramic coated pretty much any color you like,including white..... my .02
I bought a set from these people for my Pinto project. http://cgi.ebay.com/ebaymotors/Rare...r_Truck_Parts_Accessories&hash=item2a0cbc57dc They seem to have these up for sale pretty often. They would look great in that Falcon.
Lots of suppliers for fenderwell headers for your Nova. Hooker, Patriot, Dougs, and Hedman for a few. You'll have to paint them yourself.
For what it's worth, in the new Speedway catalog the small block chevy hedders are the same price as the big block hedders. Around $220.00.
If you can afford them go with Doug's Headers, I had a set on my Chevelle and they absolutely cannot be beat.