I'm not Cosworth, but I'll give you what I think the answers would be-
-There is no way they are going to produce a cast manifold that retains a dual runner design for under $1,000.
-I'd assume it will be cast aluminum so it will be strong.
-If it isn't dual runner than I don't want it. There are plenty of people willing to fab a single runner length manifold for cheap..but that has a lot of drawbacks.
-I'd imagine 5bhp will be no problem at high RPM with larger runners and a larger plenum.
-I'll bet $10 the minor grinding of the short runners I did to my stock manifold with a dremel and some expoy will have better results than the CVP (if it holds together)