If that is for a street driver, the manifold will make just as much power as headers, with none of the down sides (headers have a tendancy to leak, rust out in a few years, and are noisier.)
That may have been true for a daly driver thirty years ago but for a project car, a car that gets driven once or twice a week, is not going to have problems. The Hookers on my Fairlane are twenty three years old, no rust no leaks.
