I put the POR 20 high temp paint on my headers. Now I haven't run them yet, so I have no first hand experience, but I loaned the paint to a friend and he re-coated over another paint where it flaked off, and he hasn't had any problem.
I've used the POR 15 before, and it works great! I think this would do well, especially if you're going to use it as an intermediate step. What's great is that it only has to get to 300°F to reach full hardness, unlike other header paints that have to get to 600 or so.
The product is available online at
www.porstore.com. They have very quick shipping.