Tim,
If you look at my gallery you will see some photos of my exhaust. I like them pointing down a little but that is me. I would not powder coat the pipes, if you run Billboards the pipes gets sandblasted by what the tire picks up.
Just sandblast the pipes and then coat with
http://www.vhtpaint.com/flameproof.html
. This paint is great, you can add anytime and it does not show where you have added.
Allan