RE: Painting exhaust colors?
The reddish "rustoleum" can also be sanded for a smoother look. The photo of the (operational) NZ replica suggests that the exhaust heads and manifolds develop more corrosion and that the pipes are smoother (and less corroded). So I could selectively sand the tubes to create that effect. I'm also experimenting which how it looks if I start with the steel as a base and then dry brush on the "rust." I'll also try TFF's suggestion of the "dusting" with the reddish spray.
It really is heat discoloration rather than "rust" per se.
BTW, I was pleased to find 600˚ C paint in the hardware store...in black, gray, and silver.