I used the Rustoleum high heat paints in spray cans with great success. They cured fine. They covered the rust well after a little wire brushing and vacuuming.
Primer in Gray:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
and Aged Copper, which is like the Universal Brown but a little lighter, and more metallic.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
A lot of paints are baked off at the hot end of the manifold, but these are holding up well.