Why would I question it? He’s not selling the engine and frankly that engine will probably never end up in a car again. I’m just asking if manifolds come up for sale and what they go for.
Ok, then don't worry about it. Since the manifolds are not reproduced that I know of, they ain't gonna be cheap. They come up so seldom, I wouldn't know where to begin. Aussie headers can be had cheaper I'm sure and will produce more power.