Question(s) about cast iron cores for water/coolant

[71CHEVYSHORTBED402]

I had this blasted with some things. It might be the original housing off my 71 402, not sure. Could have been new to the truck in Feb. 1993 to be exact, when the engine was rebuilt.

I'd like to replace the clone smooth surface housing with this cast iron piece. Think I'll paint it with por15 engine orange, and a sponge brush - works well on cast iron, especially small stuff.

Got me wondering about core finishes, the interior surface was pretty corroded before it was blasted.

Let me guess, the factory "sprayed" the interiors with the top coat, or something else not expected to last....I really don't know, perhaps they figure corrosion protection in coolants good enough - not sure, so I'm asking.

That, and how would you finish the interior, if anything?

With a green observation, seems cast iron holds up up well to water, hot even better. Perhaps cores were hit with something temporary, for rust prevention during storage, hmm.