Years ago, there was an article on slantsix.org where they modified a stock slant six cast iron manifold to take a 2-barrel carb, I just looked but I can't find it. Basically, you purchased an adapter and used it as a pattern to mark the manifold then drilled a series of 1/8 inch holes around the perimeter and then broke out the center and then ground it out smooth. Maybe someone has a copy of the article. I think this also was in the slant six quarterly newsletter (pre internet)
