Been a while now, thought i'd post an update.
After some advice from jamie marsh and pat klutch, i have decided to change my intake manifold, in an attempt to cure the motors 7k power ceiling. In he meantime, a few things turned up.
and i know its a motor thread, but these things have been great...
In the end, a gato intake got the nod (thanks pat k). Unfortunately for me, i must be the first guy in the whole world to fit one to a rhd car, and the rhs brake booster has made it a bit of an adventure, especially after gato sent me a 6 1/4" runner version. This has also meant an injector change (id440 top feeds), aeromotive fpr, and some nice injector loom adapters from Eric Siu.
Was going to use my xcessive spacer again, but now going with the oem one due to space requirements
The manifold is a really good piece. Lovely straight shot at the intake port (looks bent,isn't). lovely upward angle with slight taper.
Ported heads only need apply. Looks to me like they use a similar flange to the mazworx one. 55ish mm width.
In the end, i ended up welding a plate to the bottom for the iacv again. It was just easier to fit on this way. Keen eyes might spot and rhd "mods"...