A guy I worked with at Douglas Aircraft married a gal with a Olds F85, little v8 with aluminum heads, and for a reason I can't remember pulled the valve covers. The walls around the water jackets were paper thin. He had the heads redone and found out a previous boy friend of his new wife had drained the anti freeze because he figured straight water would cool better. It will but causes havoc with dissimilar metals.
I believe the manifold can be saved but the question is whether it's worth it or not.