the old 8 valve OHC vxhall engines had that type inlet manifold
i.e c16se with idle control screw on the housing
I know on migweb some bloke designed a new inlet manifold for the x16xe engine [lotus designed], vxhall chucked on a massive inlet manifold to starve the engine of 20 bhp and reduce emissions
the bloke basically designed a metal box with 4 equal length pipes and fitment for the throttle body similar to where it sits on the SC conversion
£150 later and 10 bhp +
now that is turbo tuning figures based on that price
scot i suggest u register on migweb and do a search for it