A few years ago I restored a 1955 Jaguar XK 140 which has porcelain exhaust manifolds. I had my manifolds sandblasted removing what old porcelain was left and had them re-coated by a company somewhere in the mid west. (They advertise in Hemmings) They were really nice and helped the car to win numerous 1st place awards.
This was before all the new powder coating and ceramic applications that are now offered. I recently had a few engine pieces powder coated for a 1984 Ferrari 308 I restored. Most pieces were either silver (exhaust), red (engine parts) or black (cooling tanks and air intake box) The black is very glossy and seems to be holding up quite well. So, I suggest you talk to a powder coating company about either powder or ceramic coating. See what they say about the heat of the manifold. Or, contact a company that does the porcelain coating. Good luck and have fun!