The only thing I could potentially think of is the N/A Neo head is different - which would strike me as odd..
The r33 na and turbo heads are idential, same bolt pattern and fully interchangeable.
The R34 GT-T head is a different set-up to the R33 heads, however the manifold bolt pattern (both inlet and exhaust side) is the same as the R33 heads so the manifolds are definitely interchangeable.
I've swapped all of the above over before, but must admit I've never touched an N/A Neo head before - I would have assumed that the N/A Neo head would have the same pattern as the turbo one because thats what it is like on the R33 engine... and its unlike Nissan to develop a completely different head.
Unfortunately, if the n/a neo manifold wont fit on the S2 engine, then its no longer a simple bolt in excercise with the gear you have..
I would still steer away from running the R33 gear and re-wiring your R34 to suit but thats me.
If it was me, I would look at three options:
-try to track down a standard turbo neo manifold for cheap and bolt that onto the S2 engine.
-If you can't get the stock manifold or if they want blood money for it, then buy an aftermarket top feel fuel rail and fuel regualtor so you can run the top feed injectors on the S2 manifold. A nice rail is around $180, $50 for fittings, then $150 for a regulator - so budject around $400.
-Replace the inlet side altogether with an aftermarket set-up. Get a new Greddy "style" manfold (or the genuine version if have the $$), get an aftermaket fuel rail and regulator to suit the top feed injectors for an R33 manfiold. This will cost anywhere from $700-$1300 depending if you get the genuine greddy gear or not.