All engines were assembled with the manifolds on them,then painted.
As we all know,the paint on the manifolds lasted not long after being driven.
So,the "correct" look is..paint burned off and bare metal.
For those who prefer opening the hood like a jewelery box,using POR-15,or Eastwood's manifold paint is better looking than rusty exhaust manifolds.
Many of us have done tons of detailing under the hood and the products mentioned above have become acceptable in the hobby
In the past,I gave my logs a good blast of glass beading for the "au-natural look,LOL!As time went by they showed there true age.

This time I am using the POR-15.