Fortunately my sister saved me from that since everybody was so proud of her they never noticed what I did. She has a doctorate now and doesn't have the sense that God gave a goose. Definitely forgot what Mom taught us about getting above our raising.
To the OP. Had a set of those manifolds and studied them at length. Looks to me like most of the restriction is at the outlet where the ball for the head pipe to seal on necks the outlet size down to 1 1/2" on both manifolds. If you measure the outside of the balls it comes out to almost 2 1/4". I was thinking that if I had those balls machined off and the outlet opened up to 2 1/4" these manifolds would flow almost as good as a 340 manifold which ain't bad. Might work if you can find a flat pipe flange and a gasket that would work. Maybe Dakota parts would do the trick???