We have been using this product
https://www.cerakote.com/ on headers/exhaust, gas and brake related items and have been very happy with the out come. Lots of colors to chose from.
Most custom Fire Arms Shops are using this product. Super durable, Dissipates heat quickly, gas and brake fluid impervious. Just got to find a shop that has a big enough blast cabinet and oven to do bigger items such as headers and exhaust parts
I'll post a couple of pictures of a set of Cobra Headers and side exhaust later if you'd like.