Exhaust Manifold Painting Fail
This exercise proved to be a complete failure. I left the manifolds for several days before reinstalling, so I was confident the paint had plenty of time to dry. I fired the car up and headed out for a drive, and by the time I'd reached the first intersection there was smoke pouring from the vents on either side of the engine bay. I guessed this was the paint 'curing', and the smoke did clear after a few minutes on the road.
When I got back to the garage (after around an hour of driving) the finish on the manifolds looked matt and powdery. Once they had cooled down enough I gave them a wipe with a cloth, thinking that the powdery substance would wipe off to reveal my beautifully cured finish. What I saw instead was the raw cast iron! The paint had been cooked off completely on most of the manifold, with only the cooler sections (like the alternator mounting bracket) showing any trace of the new paint.
It's entirely possible that I messed up the application, but I was so careful. I decided that I was not going to try again, I was done with painting manifolds. I now have a barely-used can of Bill Hirsch High Temp paint for sale if anyone is interested.