Although I haven't been tuning my h20 setup, I find many people report low-mid 200's water temp.
The only suggestion I could have made was to drill the clutch shoes. Or, run a circuit pipe but I don't think that will get you exactly what you seek. The engine can get you past 40, butnot by a lot and not for a long time either. It really is screaming pretty well up there but I have gotten mine to 43 air cooled.
The real answer is to try and find an nu50 engine. My nx50 swapped NC laughed at me for bitching out and only reaching 45~ last night on a teat run of a new belt.