Attached is the photo to the manifold. I also did a test using a magnet and answer my own question. The result is that it's not brass since magnet sticks to the metal. My thought of the yellowish is rust build up over period of time and it eats away the black paint. Oh well
Used to live up north in Falmouth, cape cod, see you are in New Jersey near the ocean maybe the salt corrodes everything. My thought is spray with simple green rub it down with 0000 steel wool hit it with the ultra and you should be good.
Brian