I was a bit late on the post but dont worry about the r200 you are right with sticking with what came easily the R180.

You could also do an alloy turbo A series manifold out of billet to be use for casting into iron similar to the suzuki gti one, there will be interested parties who prefer them over tube ones that dont flow well. Ill be in for a couple, Im sure theres another dozen that would jump on them too, and doing out of cast you can do smaller runs or batches in sandcasting saving money.
http://www.ebay.com/itm/Turbo-Exhaust ... ts_SM&hash=item1e6d0498fa

you can pair the turbo manifold with something like these which could be used for carbs or add a plenum for turbo
http://blogs.yahoo.co.jp/hugo3058jp/29185558.html

I think these would be better but more angled up to clear turbo manifold and peeps can use 44mm downdraft bike carbs.
http://datsun1200.com/uploads/newbb/8618_504ec078872f1.jpg

vacuum can be made between the 2 sep pieces by brass taps and hosing to avoid billet pieces been too big to start with.

You can do a flange plate to suit these manifolds (ive poorly illustrated in 5 mins) and then any plenum from other cars can be welded up on top of the 2 hole flange with tapered holes to match the mini manifolds.

Attach file:

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  manifolds for A series.JPG (41.75 KB)


  flange for A series.JPG (17.44 KB)