[Fred Lee]

That is a 1990's marine intake manifold. The rough part of the casting by the thermostat is actually a thin covering of aluminum over a brass or bronze insert. Salt water attacks aluminum more than brass or bronze. There should be insert protection at the distributor area as well where the water passage comes out of the cylinder head.
I do have a replacement or superceded #163 intake manifold that was a take off or nearly new. I would sell if it meant making a clone car more correct. Fred Lee 231-740-5534
Cell phone.