Dang, I wished I had found out about that stuff beforeI just finished painting my new manifolds. I ordered some Por-20 brilliant aluminum (basically high temp paint) I don't think it will do anything to keep heat down, but it is supposed to keep the manifolds looking good and free from corrosion. I still have a ton left caleb if you want to try some.
I looked into the HPC coating and found it was too expensive for me to be justified. I think they sandblast before coating anyways, so you could try about anything and still go back to HPC.
EZ