It's not necessarily the paint itself so much as it is the surface preparation.
For the valve covers, I'd scrape as much paint off as possible and then sand the surface lightly. Apply a good autobody primer and then hit it with a spray of Tremclad or something similar.
The exhaust is another matter, as the temperatures here get high enough to destroy any type of paint put on the surface. I'm not aware of any type of DIY paint system that is durable enough to use on exhaust components.
For the valve covers, I'd scrape as much paint off as possible and then sand the surface lightly. Apply a good autobody primer and then hit it with a spray of Tremclad or something similar.
The exhaust is another matter, as the temperatures here get high enough to destroy any type of paint put on the surface. I'm not aware of any type of DIY paint system that is durable enough to use on exhaust components.