Exhaust heat shield, paint?

See that's why the year make and model should be stated from the beginning. A warmed air / heat stove isn't applicable to a 67 273. Need not have been mentioned.
I have the same 273 heat shields here and they have the same gloss black on them. Its a higher gloss than we see on most sheet metals, like body panels. Maybe they weren't painted before delivery in quantities to engine plants,,,, maybe even yes to Plymouth but no to Dodge.
They were painted when packaged/sent to the dealers replacement parts inventory. That is where mine came from.