maybe 15 or 20 years ago, there was a huge electric oven at work.
i blasted as set of headers of unknown brand, then doused them real good with dupli-color black ceramic 1200 degree spray can stuff, blasting the collector/primary tube connection real good.
i then stuck them into that oven and baked them at 450 degrees for 2 hours. [the can says 400 degrees for 1 1/2 hours, or 600 degrees for 1 hour]
they turned out real good, and still look good today, with the exception of a couple scrapes and oil spills.
i believe the secret of any high temperature coating is in the preparation, just like any high end paint job.
i also did the mufflers [flowcrapster], the mandrel bend, fabricated tail pipes, and the muffler clamps. [the new style stainless band clamps were not available back then]
i wished i had done the straight sections of 3" tube from the headers to the mufflers, but i didn't because they were aluminized pipe.
it all depends on the person doing the job.
just my personal life experience. your mileage will vary.