My experience is the same as Nuno’s – if the car’s alignment isn’t out of whack, it’s totally stable above 180 mph even with stock aerodynamics. On tarmac, at least. I don't know about salt.
With 600 rear wheel hp, you should have no problem getting to 200 mph if your gearing is long enough. Fixed-headlight NA2s put about 250 of their 290 hp to the road and those 250 rwhp are enough to push the car to 174 mph. If you increase the horsepower making it to the road by 140%, that should be enough to overcome wind resistance at a 34% higher speed. In other words, 600 rear wheel hp should be enough to push a fixed-headlight NA2 with stock aerodynamics through the wind at 233 mph.
Since you have a widebody, the question is how much higher your drag is. NSX owner Yankee here on Prime did a top speed test of his NA1 five speed widebody with a GT500 rear wing. His top speed was 242 km/h in both fourth and fifth gears. In fifth, his rpm were stable at around 6200 (he had larger than stock wheels/tires). At that speed, a stock NA1 five speed engine should be putting out around 251 crank hp. If Yankee got 242 km/h out of 251 crank hp, that implies that his car had about 29% more drag than a stock pop-up headlight NSX. There are several “ifs” in that calculation, but it may yield a ballpark estimate of the relative drag of a widebody NSX with a GT500 rear wing.
So, if a stock NA1 five speed with 235 rwhp can get to 168 mph, an NSX with 29% more drag than that but 600 rwhp should be able to get to 211 mph – just like Ruf’s “Yellowbird”. Provided the gearing is long enough that the car hits top speed when the engine is producing maximum power.
None of the SoS widebody body parts look egregiously drag-inducing except for that big rear wing. Have a look at
this test. If you just buy a used stock rear trunk lid for your top speed runs and get looooong gearing, you could probably go faster than Ruf’s “Yellowbird”. And then someone can shoot a film that gearheads will love titled “The World’s Fastest NSX”!