I agree with Rob, Jet-hot coating works great. It also helps to conduct heat away from the heads and out of the engine compartment. Looks last a long time too.
http://www.jet-hot.com/
Three inch mandrel bent works great for flow. Sounds great with Flowmaster mufflers, too. After I drove my Chevelle this way for a year, I added "bullet" mufflers to the system to reduce the resonance - but it was my daily driver at the time!